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* How to checking the existance of constraints for a table?
@ 2011-02-02 20:40 creationw <mr.creation.register@gmail.com>
0 siblings, 1 reply; 2+ messages in thread
From: creationw @ 2011-02-02 20:40 UTC (permalink / raw)
To: pgsql-sql
Hello,
I have a sample table describe as follows, anyone knows how to checking the
existence of a constraint?
oviddb=# \d myTable
Column | Type | Modifiers
---------+----------+-----------
orderid | smallint | not null
modelid | smallint | not null
Indexes:
"mytable_orderid_key" UNIQUE, btree (orderid)
For example, how to know that myTable has a constraint with name
"mytable_orderid_key"?
I have this problem because when doing migration script, some old table may
have this constraint or may not have. And after migration, we want to add
this constraint:
If I just run the command:
alter table myTable add Unique (orderid) in the migration script, when the
constraint exits, a new index will be created as
"mytable_orderid_key1" UNIQUE, btree (orderid)
So, it causes some duplication.
oviddb=# \d myTable
Column | Type | Modifiers
---------+----------+-----------
orderid | smallint | not null
modelid | smallint | not null
Indexes:
"mytable_orderid_key" UNIQUE, btree (orderid)
"mytable_orderid_key1" UNIQUE, btree (orderid)
My question becomes how to write sql statement with following semantecs
if constraint unique (orderid) exists
do nothing
else
alter table myTable add Unique (orderid)
Thank you so much!
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* Re: How to checking the existance of constraints for a table?
@ 2011-02-04 16:38 bricklen <bricklen@gmail.com>
parent: creationw <mr.creation.register@gmail.com>
0 siblings, 0 replies; 2+ messages in thread
From: bricklen @ 2011-02-04 16:38 UTC (permalink / raw)
To: creationw <mr.creation.register@gmail.com>; +Cc: pgsql-sql
On Wed, Feb 2, 2011 at 12:40 PM, creationw
<mr.creation.register@gmail.com> wrote:
>
> Hello,
>
> I have a sample table describe as follows, anyone knows how to checking the
> existence of a constraint?
>
> oviddb=# \d myTable
>
> Column | Type | Modifiers
> ---------+----------+-----------
> orderid | smallint | not null
> modelid | smallint | not null
>
> Indexes:
> "mytable_orderid_key" UNIQUE, btree (orderid)
>
> For example, how to know that myTable has a constraint with name
> "mytable_orderid_key"?
You could try checking the information_schema.table_constraints view.
Eg. select * from information_schema.table_constraints where
table_name='myTable'
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