CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions
Attached is my work in progress to implement the changes to the CAST()
function as proposed by Vik Fearing.
This work builds upon the Error-safe User Functions work currently ongoing.
The proposed changes are as follows:
CAST(expr AS typename)
continues to behave as before.
CAST(expr AS typename ERROR ON ERROR)
has the identical behavior as the unadorned CAST() above.
CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.
CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.
There is an additional FORMAT parameter that I have not yet implemented, my
understanding is that it is largely intended for DATE/TIME field
conversions, but others are certainly possible.
CAST(expr AS typename FORMAT fmt DEFAULT expr2 ON ERROR)
What is currently working:
- Any scalar expression that can be evaluated at parse time. These tests
from cast.sql all currently work:
VALUES (CAST('error' AS integer));
VALUES (CAST('error' AS integer ERROR ON ERROR));
VALUES (CAST('error' AS integer NULL ON ERROR));
VALUES (CAST('error' AS integer DEFAULT 42 ON ERROR));
SELECT CAST('{123,abc,456}' AS integer[] DEFAULT '{-789}' ON ERROR) as
array_test1;
- Scalar values evaluated at runtime.
CREATE TEMPORARY TABLE t(t text);
INSERT INTO t VALUES ('a'), ('1'), ('b'), (2);
SELECT CAST(t.t AS integer DEFAULT -1 ON ERROR) AS foo FROM t;
foo
-----
-1
1
-1
2
(4 rows)
Along the way, I made a few design decisions, each of which is up for
debate:
First, I created OidInputFunctionCallSafe, which is to OidInputFunctionCall
what InputFunctionCallSafe is to InputFunctionCall. Given that the only
place I ended up using it was stringTypeDatumSafe(), it may be possible to
just move that code inside stringTypeDatumSafe.
Next, I had a need for FuncExpr, CoerceViaIO, and ArrayCoerce to all report
if their expr argument failed, and if not, just past the evaluation of
expr2. Rather than duplicate this logic in several places, I chose instead
to modify CoalesceExpr to allow for an error-test mode in addition to its
default null-test mode, and then to provide this altered node with two
expressions, the first being the error-safe typecast of expr and the second
being the non-error-safe typecast of expr2.
I still don't have array-to-array casts working, as the changed I would
likely need to make to ArrayCoerce get somewhat invasive, so this seemed
like a good time to post my work so far and solicit some feedback beyond
what I've already been getting from Jeff Davis and Michael Paquier.
I've sidestepped domains as well for the time being as well as avoiding JIT
issues entirely.
No documentation is currently prepared. All but one of the regression test
queries work, the one that is currently failing is:
SELECT CAST('{234,def,567}'::text[] AS integer[] DEFAULT '{-1011}' ON
ERROR) as array_test2;
Other quirks:
- an unaliased CAST ON DEFAULT will return the column name of "coalesce",
which internally is true, but obviously would be quite confusing to a user.
As a side observation, I noticed that the optimizer already tries to
resolve expressions based on constants and to collapse expression trees
where possible, which makes me wonder if the work done to do the same in
transformTypeCast/ and coerce_to_target_type and coerce_type isn't also
wasted.
Attachments:
0003-CAST-ON-DEFAULT-work-in-progress.patchtext/x-patch; charset=US-ASCII; name=0003-CAST-ON-DEFAULT-work-in-progress.patchDownload+551-159
0001-add-OidInputFunctionCall.patchtext/x-patch; charset=US-ASCII; name=0001-add-OidInputFunctionCall.patchDownload+17-1
0002-add-stringTypeDatumSafe.patchtext/x-patch; charset=US-ASCII; name=0002-add-stringTypeDatumSafe.patchDownload+15-1
Corey Huinker <corey.huinker@gmail.com> writes:
The proposed changes are as follows:
CAST(expr AS typename)
continues to behave as before.
CAST(expr AS typename ERROR ON ERROR)
has the identical behavior as the unadorned CAST() above.
CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.
CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.
While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.
If we know that they are about to standardize exactly this syntax,
where is that information available? If we don't know that,
I'd prefer to invent some kind of function or other instead of
extending the grammar.
regards, tom lane
On Tue, 20 Dec 2022 at 04:27, Corey Huinker <corey.huinker@gmail.com> wrote:
Attached is my work in progress to implement the changes to the CAST() function as proposed by Vik Fearing.
This work builds upon the Error-safe User Functions work currently ongoing.
The proposed changes are as follows:
CAST(expr AS typename)
continues to behave as before.CAST(expr AS typename ERROR ON ERROR)
has the identical behavior as the unadorned CAST() above.CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return NULL if the cast fails.CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return expr2 if the cast fails.There is an additional FORMAT parameter that I have not yet implemented, my understanding is that it is largely intended for DATE/TIME field conversions, but others are certainly possible.
CAST(expr AS typename FORMAT fmt DEFAULT expr2 ON ERROR)What is currently working:
- Any scalar expression that can be evaluated at parse time. These tests from cast.sql all currently work:VALUES (CAST('error' AS integer));
VALUES (CAST('error' AS integer ERROR ON ERROR));
VALUES (CAST('error' AS integer NULL ON ERROR));
VALUES (CAST('error' AS integer DEFAULT 42 ON ERROR));SELECT CAST('{123,abc,456}' AS integer[] DEFAULT '{-789}' ON ERROR) as array_test1;
- Scalar values evaluated at runtime.
CREATE TEMPORARY TABLE t(t text);
INSERT INTO t VALUES ('a'), ('1'), ('b'), (2);
SELECT CAST(t.t AS integer DEFAULT -1 ON ERROR) AS foo FROM t;
foo
-----
-1
1
-1
2
(4 rows)Along the way, I made a few design decisions, each of which is up for debate:
First, I created OidInputFunctionCallSafe, which is to OidInputFunctionCall what InputFunctionCallSafe is to InputFunctionCall. Given that the only place I ended up using it was stringTypeDatumSafe(), it may be possible to just move that code inside stringTypeDatumSafe.
Next, I had a need for FuncExpr, CoerceViaIO, and ArrayCoerce to all report if their expr argument failed, and if not, just past the evaluation of expr2. Rather than duplicate this logic in several places, I chose instead to modify CoalesceExpr to allow for an error-test mode in addition to its default null-test mode, and then to provide this altered node with two expressions, the first being the error-safe typecast of expr and the second being the non-error-safe typecast of expr2.
I still don't have array-to-array casts working, as the changed I would likely need to make to ArrayCoerce get somewhat invasive, so this seemed like a good time to post my work so far and solicit some feedback beyond what I've already been getting from Jeff Davis and Michael Paquier.
I've sidestepped domains as well for the time being as well as avoiding JIT issues entirely.
No documentation is currently prepared. All but one of the regression test queries work, the one that is currently failing is:
SELECT CAST('{234,def,567}'::text[] AS integer[] DEFAULT '{-1011}' ON ERROR) as array_test2;
Other quirks:
- an unaliased CAST ON DEFAULT will return the column name of "coalesce", which internally is true, but obviously would be quite confusing to a user.As a side observation, I noticed that the optimizer already tries to resolve expressions based on constants and to collapse expression trees where possible, which makes me wonder if the work done to do the same in transformTypeCast/ and coerce_to_target_type and coerce_type isn't also wasted.
CFBot shows some compilation errors as in [1]https://cirrus-ci.com/task/6687753371385856?logs=gcc_warning#L448, please post an updated
version for the same:
[02:53:44.829] time make -s -j${BUILD_JOBS} world-bin
[02:55:41.164] llvmjit_expr.c: In function ‘llvm_compile_expr’:
[02:55:41.164] llvmjit_expr.c:928:6: error: ‘v_resnull’ undeclared
(first use in this function); did you mean ‘v_resnullp’?
[02:55:41.164] 928 | v_resnull = LLVMBuildLoad(b, v_reserrorp, "");
[02:55:41.164] | ^~~~~~~~~
[02:55:41.164] | v_resnullp
[02:55:41.164] llvmjit_expr.c:928:6: note: each undeclared identifier
is reported only once for each function it appears in
[02:55:41.164] llvmjit_expr.c:928:35: error: ‘v_reserrorp’ undeclared
(first use in this function); did you mean ‘v_reserror’?
[02:55:41.164] 928 | v_resnull = LLVMBuildLoad(b, v_reserrorp, "");
[02:55:41.164] | ^~~~~~~~~~~
[02:55:41.164] | v_reserror
[02:55:41.165] make[2]: *** [<builtin>: llvmjit_expr.o] Error 1
[02:55:41.165] make[2]: *** Waiting for unfinished jobs....
[02:55:45.495] make[1]https://cirrus-ci.com/task/6687753371385856?logs=gcc_warning#L448: *** [Makefile:42: all-backend/jit/llvm-recurse] Error 2
[02:55:45.495] make: *** [GNUmakefile:21: world-bin-src-recurse] Error 2
[1]: https://cirrus-ci.com/task/6687753371385856?logs=gcc_warning#L448
Regards,
Vignesh
On 2023-01-02 Mo 10:57, Tom Lane wrote:
Corey Huinker <corey.huinker@gmail.com> writes:
The proposed changes are as follows:
CAST(expr AS typename)
continues to behave as before.
CAST(expr AS typename ERROR ON ERROR)
has the identical behavior as the unadorned CAST() above.
CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.
CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.
If we know that they are about to standardize exactly this syntax,
where is that information available? If we don't know that,
I'd prefer to invent some kind of function or other instead of
extending the grammar.
+1
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com
On Mon, Jan 2, 2023 at 10:57 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Corey Huinker <corey.huinker@gmail.com> writes:
The proposed changes are as follows:
CAST(expr AS typename)
continues to behave as before.
CAST(expr AS typename ERROR ON ERROR)
has the identical behavior as the unadorned CAST() above.
CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.
CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.
If we know that they are about to standardize exactly this syntax,
where is that information available? If we don't know that,
I'd prefer to invent some kind of function or other instead of
extending the grammar.regards, tom lane
I'm going off the spec that Vik presented in
/messages/by-id/f8600a3b-f697-2577-8fea-f40d3e18bea8@postgresfriends.org
which is his effort to get it through the SQL committee. I was
alreading thinking about how to get the SQLServer TRY_CAST() function into
postgres, so this seemed like the logical next step.
While the syntax may change, the underlying infrastructure would remain
basically the same: we would need the ability to detect that a typecast had
failed, and replace it with the default value, and handle that at parse
time, or executor time, and handle array casts where the array has the
default but the underlying elements can't.
It would be simple to move the grammar changes to their own patch if that
removes a barrier for people.
Corey Huinker <corey.huinker@gmail.com> writes:
On Mon, Jan 2, 2023 at 10:57 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.
I'm going off the spec that Vik presented in
/messages/by-id/f8600a3b-f697-2577-8fea-f40d3e18bea8@postgresfriends.org
which is his effort to get it through the SQL committee.
I'm pretty certain that sending something to pgsql-hackers will have
exactly zero impact on the SQL committee. Is there anything actually
submitted to the committee, and if so what's its status?
regards, tom lane
On 1/3/23 19:14, Tom Lane wrote:
Corey Huinker <corey.huinker@gmail.com> writes:
On Mon, Jan 2, 2023 at 10:57 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
While I approve of trying to get some functionality in this area,
I'm not sure that extending CAST is a great idea, because I'm afraid
that the SQL committee will do something that conflicts with it.I'm going off the spec that Vik presented in
/messages/by-id/f8600a3b-f697-2577-8fea-f40d3e18bea8@postgresfriends.org
which is his effort to get it through the SQL committee.I'm pretty certain that sending something to pgsql-hackers will have
exactly zero impact on the SQL committee. Is there anything actually
submitted to the committee, and if so what's its status?
I have not posted my paper to the committee yet, but I plan to do so
before the working group's meeting early February. Just like with
posting patches here, I cannot guarantee that it will get accepted but I
will be arguing for it.
I don't think we should add that syntax until I do get it through the
committee, just in case they change something.
--
Vik Fearing
Vik Fearing <vik@postgresfriends.org> writes:
I have not posted my paper to the committee yet, but I plan to do so
before the working group's meeting early February. Just like with
posting patches here, I cannot guarantee that it will get accepted but I
will be arguing for it.
I don't think we should add that syntax until I do get it through the
committee, just in case they change something.
Agreed. So this is something we won't be able to put into v16;
it'll have to wait till there's something solid from the committee.
regards, tom lane
On Tue, 3 Jan 2023 at 14:16, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Vik Fearing <vik@postgresfriends.org> writes:
I don't think we should add that syntax until I do get it through the
committee, just in case they change something.Agreed. So this is something we won't be able to put into v16;
it'll have to wait till there's something solid from the committee.
I guess I'll mark this Rejected in the CF then. Who knows when the SQL
committee will look at this...
--
Gregory Stark
As Commitfest Manager
On Mon, 19 Dec 2022 at 17:57, Corey Huinker <corey.huinker@gmail.com> wrote:
Attached is my work in progress to implement the changes to the CAST()
function as proposed by Vik Fearing.CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.
Is there any difference between NULL and DEFAULT NULL?
On Tue, Mar 28, 2023 at 2:53 PM Gregory Stark (as CFM) <stark.cfm@gmail.com>
wrote:
On Tue, 3 Jan 2023 at 14:16, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Vik Fearing <vik@postgresfriends.org> writes:
I don't think we should add that syntax until I do get it through the
committee, just in case they change something.Agreed. So this is something we won't be able to put into v16;
it'll have to wait till there's something solid from the committee.I guess I'll mark this Rejected in the CF then. Who knows when the SQL
committee will look at this...--
Gregory Stark
As Commitfest Manager
Yes, for now. I'm in touch with the pg-people on the committee and will
resume work when there's something to act upon.
On Tue, Mar 28, 2023 at 3:25 PM Isaac Morland <isaac.morland@gmail.com>
wrote:
On Mon, 19 Dec 2022 at 17:57, Corey Huinker <corey.huinker@gmail.com>
wrote:Attached is my work in progress to implement the changes to the CAST()
function as proposed by Vik Fearing.CAST(expr AS typename NULL ON ERROR)
will use error-safe functions to do the cast of expr, and will return
NULL if the cast fails.CAST(expr AS typename DEFAULT expr2 ON ERROR)
will use error-safe functions to do the cast of expr, and will return
expr2 if the cast fails.Is there any difference between NULL and DEFAULT NULL?
What I think you're asking is: is there a difference between these two
statements:
SELECT CAST(my_string AS integer NULL ON ERROR) FROM my_table;
SELECT CAST(my_string AS integer DEFAULT NULL ON ERROR) FROM my_table;
And as I understand it, the answer would be no, there is no practical
difference. The first case is just a convenient shorthand, whereas the
second case tees you up for a potentially complex expression. Before you
ask, I believe the ON ERROR syntax could be made optional. As I implemented
it, both cases create a default expression which then typecast to integer,
and in both cases that expression would be a const-null, so the optimizer
steps would very quickly collapse those steps into a plain old constant.
hi.
more preparation work has been committed.
1. SQL/JSON patch [1]https://git.postgresql.org/cgit/postgresql.git/diff/src/backend/parser/gram.y?id=6185c9737cf48c9540782d88f12bd2912d6ca1cc added keyword ERROR
2. CoerceViaIo, CoerceToDomain can be evaluated error safe. see commit [2]https://git.postgresql.org/cgit/postgresql.git/commit/?id=aaaf9449ec6be62cb0d30ed3588dc384f56274bf.
3. ExprState added ErrorSaveContext point, so before calling ExecInitExprRec
set valid ErrorSaveContext for ExprState->escontext we should evaluate
expression error softly.
see commit [2]https://git.postgresql.org/cgit/postgresql.git/commit/?id=aaaf9449ec6be62cb0d30ed3588dc384f56274bf also.
I only found oracle implement, [3]https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/CAST.html.
Based on my reading of [4]https://peter.eisentraut.org/blog/2023/04/04/sql-2023-is-finished-here-is-whats-new, it seems CAST(EXPRESSION AS TYPE DEFAULT
def_expr ON ERROR)
is not included in SQL:2023.
anyway, just share my POC based on the previous patch in this thread.
it will work for domain over composite, composite over domain.
example:
CREATE DOMAIN d_char3_not_null as char(3) NOT NULL;
CREATE TYPE comp_domain_with_typmod AS (a d_char3_not_null, b int);
SELECT CAST('(,42)' AS comp_domain_with_typmod DEFAULT NULL ON ERROR);
--return NULL
[1]: https://git.postgresql.org/cgit/postgresql.git/diff/src/backend/parser/gram.y?id=6185c9737cf48c9540782d88f12bd2912d6ca1cc
[2]: https://git.postgresql.org/cgit/postgresql.git/commit/?id=aaaf9449ec6be62cb0d30ed3588dc384f56274bf
[3]: https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/CAST.html
[4]: https://peter.eisentraut.org/blog/2023/04/04/sql-2023-is-finished-here-is-whats-new
Attachments:
v1-0001-make-ArrayCoerceExpr-error-safe.patchtext/x-patch; charset=US-ASCII; name=v1-0001-make-ArrayCoerceExpr-error-safe.patchDownload+14-1
v1-0002-CAST-expr-AS-newtype-DEFAULT-ON-ERROR.patchtext/x-patch; charset=US-ASCII; name=v1-0002-CAST-expr-AS-newtype-DEFAULT-ON-ERROR.patchDownload+769-3
On 22/07/2025 03:59, jian he wrote:
Based on my reading of [4], it seems CAST(EXPRESSION AS TYPE DEFAULT
def_expr ON ERROR)
is not included in SQL:2023.[4]https://peter.eisentraut.org/blog/2023/04/04/sql-2023-is-finished-here-is-whats-new
It was accepted into the standard after 2023 was released. I am the
author of this change in the standard, so feel free to ask me anything
you're unsure about.
--
Vik Fearing
On Tue, Jul 22, 2025 at 2:45 PM Vik Fearing <vik@postgresfriends.org> wrote:
It was accepted into the standard after 2023 was released. I am the
author of this change in the standard, so feel free to ask me anything
you're unsure about.
is the generally syntax as mentioned in this thread:
CAST(source_expression AS target_type DEFAULT default_expression ON ERROR)
if so, what's the restriction of default_expression?
On 22/07/2025 12:19, jian he wrote:
On Tue, Jul 22, 2025 at 2:45 PM Vik Fearing <vik@postgresfriends.org> wrote:
It was accepted into the standard after 2023 was released. I am the
author of this change in the standard, so feel free to ask me anything
you're unsure about.is the generally syntax as mentioned in this thread:
CAST(source_expression AS target_type DEFAULT default_expression ON ERROR)if so, what's the restriction of default_expression?
The actual syntax is:
<cast specification> ::=
CAST <left paren>
<cast operand> AS <cast target>
[ FORMAT <cast template> ]
[ <cast error behavior> ON CONVERSION ERROR ]
<right paren>
"CONVERSION" is probably a noise word, but it is there because A) Oracle
wanted it there, and B) it makes sense because if the <cast error
behavior> fails, that is still a failure of the entire CAST.
The <cast error behavior> is:
<cast error behavior> ::=
ERROR
| NULL
| DEFAULT <value expression>
but I am planning on removing the NULL variant in favor of having the
<value expression> be a <contextually typed value specification>. So it
would be either ERROR ON CONVERSION ERROR (postgres's current behavior),
or DEFAULT NULL ON CONVERSION ERROR.
An example of B) above would be: CAST('five' AS INTEGER DEFAULT 'six' ON
CONVERSION ERROR). 'six' is no more an integer than 'five' is, so that
would error out because the conversion error does not happen on the
operand but on the default clause. CAST('five' AS INTEGER DEFAULT 6 ON
CONVERSION ERROR) would work.
--
Vik Fearing
On 22/07/2025 14:26, Vik Fearing wrote:
The <cast error behavior> is:
<cast error behavior> ::=
ERROR
| NULL
| DEFAULT <value expression>but I am planning on removing the NULL variant in favor of having the
<value expression> be a <contextually typed value specification>. So
it would be either ERROR ON CONVERSION ERROR (postgres's current
behavior), or DEFAULT NULL ON CONVERSION ERROR.
Sorry, I meant <implicitly typed value specification>.
The point being that CAST(ARRAY['1', '2', 'three'] AS INTEGER ARRAY
DEFAULT NULL ON CONVERSION ERROR) will give you (CAST NULL AS INTEGER
ARRAY) and *not* ARRAY[1, 2, NULL].
--
Vik Fearing
On Tue, Jul 22, 2025 at 2:45 AM Vik Fearing <vik@postgresfriends.org> wrote:
On 22/07/2025 03:59, jian he wrote:
Based on my reading of [4], it seems CAST(EXPRESSION AS TYPE DEFAULT
def_expr ON ERROR)
is not included in SQL:2023.[4]
https://peter.eisentraut.org/blog/2023/04/04/sql-2023-is-finished-here-is-whats-new
It was accepted into the standard after 2023 was released. I am the
author of this change in the standard, so feel free to ask me anything
you're unsure about.
That's excellent news. I was already planning on retrying this for v19, but
I'll try sooner now.
On Tue, Jul 22, 2025 at 8:26 PM Vik Fearing <vik@postgresfriends.org> wrote:
The actual syntax is:
<cast specification> ::=
CAST <left paren>
<cast operand> AS <cast target>
[ FORMAT <cast template> ]
[ <cast error behavior> ON CONVERSION ERROR ]
<right paren>"CONVERSION" is probably a noise word, but it is there because A) Oracle
wanted it there, and B) it makes sense because if the <cast error
behavior> fails, that is still a failure of the entire CAST.The <cast error behavior> is:
<cast error behavior> ::=
ERROR
| NULL
| DEFAULT <value expression>but I am planning on removing the NULL variant in favor of having the
<value expression> be a <contextually typed value specification>. So it
would be either ERROR ON CONVERSION ERROR (postgres's current behavior),
or DEFAULT NULL ON CONVERSION ERROR.An example of B) above would be: CAST('five' AS INTEGER DEFAULT 'six' ON
CONVERSION ERROR). 'six' is no more an integer than 'five' is, so that
would error out because the conversion error does not happen on the
operand but on the default clause. CAST('five' AS INTEGER DEFAULT 6 ON
CONVERSION ERROR) would work.
hi.
<cast error behavior> ::=
ERROR
| NULL
| DEFAULT <value expression>
for <value expression>
I disallow it from returning a set, or using aggregate or window functions.
For example, the following three cases will fail:
+SELECT CAST('a' as int DEFAULT sum(1) ON CONVERSION ERROR); --error
+SELECT CAST('a' as int DEFAULT sum(1) over() ON CONVERSION ERROR); --error
+SELECT CAST('a' as int DEFAULT ret_setint() ON CONVERSION ERROR) --error
(ret_setint function is warped as (select 1 union all select 2))for array coerce, which you already mentioned, i think the following
is what we expected.
+SELECT CAST('{234,def,567}'::text[] AS integer[] DEFAULT '{-1011}' ON
CONVERSION ERROR);
+ int4
+---------
+ {-1011}
+(1 row)I didn't implement the [ FORMAT <cast template> ] part for now.
please check the attached regress test and tests expected result.
On Tue, Jul 22, 2025 at 8:26 PM Vik Fearing <vik@postgresfriends.org> wrote:
On 22/07/2025 12:19, jian he wrote:
On Tue, Jul 22, 2025 at 2:45 PM Vik Fearing <vik@postgresfriends.org> wrote:
It was accepted into the standard after 2023 was released. I am the
author of this change in the standard, so feel free to ask me anything
you're unsure about.is the generally syntax as mentioned in this thread:
CAST(source_expression AS target_type DEFAULT default_expression ON ERROR)if so, what's the restriction of default_expression?
The actual syntax is:
<cast specification> ::=
CAST <left paren>
<cast operand> AS <cast target>
[ FORMAT <cast template> ]
[ <cast error behavior> ON CONVERSION ERROR ]
<right paren>"CONVERSION" is probably a noise word, but it is there because A) Oracle
wanted it there, and B) it makes sense because if the <cast error
behavior> fails, that is still a failure of the entire CAST.The <cast error behavior> is:
<cast error behavior> ::=
ERROR
| NULL
| DEFAULT <value expression>
hi.
just want to confirm my understanding of ``[ FORMAT <cast template> ]``.
SELECT CAST('2022-13-32' AS DATE FORMAT 'YYYY-MM-DD' DEFAULT NULL ON
CONVERSION ERROR);
will return NULL.
because ``SELECT to_date('2022-13-32', 'YYYY-MM-DD');``
will error out, so the above query will fall back to the DEFAULT
expression evaluation.
