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Related blogs
PostgreSQL, MySQL or SQLiteAdding a year in PostgreSQL
Creating a user for postgresql
List of casts in PostgreSQL
Running simple SQL commands on the command line
Date formatting in python or in PostgreSQL
Integer division in programming languages
Just Oracle and IBM?
ALTER TABLE patch
Quick PostgreSQL optimization story
Date formatting in Python or in PostgreSQL (part II)
Sorting transform function in PostgreSQL
Why bother with MySQL...
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pg_class to check if table exists
http://www.vitavoom.com/postgresql-docs/catalog-pg-class.htmlpg_class, postgresql, exception, iso
20th of April 2005
I just learnt a better way to check if a PostgreSQL table exists. Before I did this to find out if table mytable is defined:
SELECT * FROM 'mytable' LIMIT 1;
But this had to be wrapped in exception catching application code because I was able to tell if the table existed if the select statement worked. That's the wrong and naive way. The correct way is to use pg_class and look at how many rows were returned:
SELECT relname FROM pg_class
WHERE relname = 'mytable';
WHERE relname = 'mytable';
Why have I missed this before? No explanation?
A disadvantage with using pg_class is that it's not ISO standard, meaning that it's specific to PostgreSQL only. The first pattern will work on all relational databases.
Comment
dd -
10th May 2006
[«« Reply to this]
For functionality similar to mysql SHOW TABLES use: select * from information_schema.tables where table_schema='public' and table_type='BASE TABLE' .
For functionality similar to mysql SHOW TABLES use: select * from information_schema.tables where table_schema='public' and table_type='BASE TABLE' .
toruvinn -
5th September 2006
[«« Reply to this]
btw. there's a problem with temporary tables, cause they might not be visible (even though they exist). it's better to use:
SELECT 1 FROM pg_catalog.pg_class WHERE relkind = 'r' AND relname = 'name' AND pg_catalog.pg_table_is_visible(oid) LIMIT 1
btw. there's a problem with temporary tables, cause they might not be visible (even though they exist). it's better to use:
SELECT 1 FROM pg_catalog.pg_class WHERE relkind = 'r' AND relname = 'name' AND pg_catalog.pg_table_is_visible(oid) LIMIT 1
In psql do "\set ECHO_HIDDEN t" and you can see all the queries it uses for the special backslash commands (like \d)