Syntax error needs fresh eyeballs

Rich Shepard <rshepard@appl-ecosys.com> writes:

My schema includes three tables and psql throws an error I'm not seeing
when I try to read the schema into the database. I'd appreciate fresh eyes
looking at the table and learning what error I'm not seeing.

Hm, seems straightforward enough to me: the only uniqueness constraint
you've got in Weather_Params is

PRIMARY KEY (site_id, param)

but in Weather_Data you write

param TEXT
REFERENCES Weather_Params(param),

so you get this

ERROR: there is no unique constraint matching given keys for referenced
table "weather_params".

because Weather_Params.param isn't constrained to be unique.
Weather_Params' pkey constrains the combination of site_id and param to be
unique, but that doesn't make param alone unique, so param in Weather_Data
isn't enough to reference a well-defined row of Weather_Params.

Seeing that Weather_Data also has a site_id column, I'm going to guess
that what you wanted to put in Weather_Data is a two-column FK:

FOREIGN KEY (site_id, param) REFERENCES Weather_Params (site_id, param)

That would match Weather_Params' pkey, so it's enough to identify a
unique row of Weather_Params.

regards, tom lane

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From: Rich Shepard
My schema includes three tables and psql throws an error I'm not seeing
when I try to read the schema into the database. I'd appreciate fresh eyes
looking at the table and learning what error I'm not seeing.

The tables:

CREATE TABLE Weather (

site_id INTEGER PRIMARY KEY,

site_name TEXT,

site_location TEXT

);

CREATE TABLE Weather_Params (

site_id INTEGER

REFERENCES Weather(site_id),

param TEXT,

param_unit TEXT,

freq INTEGER,

freq_unit TEXT,

equip TEXT,

PRIMARY KEY (site_id, param)

);

CREATE TABLE Weather_Data (

site_id INTEGER

REFERENCES Weather(site_id),

monit_date DATE,

monit_time TIME,

read_by TEXT, -- name of employee collecting data

param TEXT

REFERENCES Weather_Params(param),

param_value REAL,

PRIMARY KEY (site_id, monit_date, monit_time, param) );

The error: ERROR: there is no unique constraint matching given keys for
referenced table "weather_params".

-----------------------

Just a guess...You've camel-cased the table names but aren't using double
quotes. Try either lower-casing all table names and references to them, or
double-quoting all identifiers.

Mike

On Mon, 26 Dec 2016, Tom Lane wrote:

ERROR: there is no unique constraint matching given keys for referenced
table "weather_params".

because Weather_Params.param isn't constrained to be unique.

...

Seeing that Weather_Data also has a site_id column, I'm going to guess
that what you wanted to put in Weather_Data is a two-column FK:

FOREIGN KEY (site_id, param) REFERENCES Weather_Params (site_id, param)

That would match Weather_Params' pkey, so it's enough to identify a
unique row of Weather_Params.

Thanks, Tom. Yes, I do want a 2-column FK.

Much appreciated,

Rich

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