String Concatenation

Database Syntax
Oracle 'foo'||'bar'
Microsoft 'foo'+'bar'
PostgreSQL 'foo'||'bar'
MySQL 'foo' 'bar'
CONCAT('foo','bar')

Substring

Note that offset is 1-indexed.

Database Syntax
Oracle SUBSTR('foobar', offset, len)
Microsoft SUBSTRING('foobar', offset, len)
PostgreSQL SUBSTRING('foobar', offset, len)
MySQL SUBSTRING('foobar', offset, len)

Comments

Database Syntax
Oracle --comment
Microsoft --comment
/*comment*/
PostgreSQL --comment
/*comment*/
MySQL #comment
-- comment [Note the space after the double dash]
(use -- - if no written comment just to be safe)
/*comment*/

Quirks

Database Note
Oracle SELECT statements must have a FROM clause. You can always use FROM dual if your query doesn’t actually require a table

References

Database Version

Database Query
Oracle SELECT banner FROM v$version
SELECT version FROM v$instance
Microsoft SELECT @@version
PostgreSQL SELECT version()
MySQL SELECT @@version

Database Contents

Database Query
Oracle SELECT * FROM all_tables
SELECT * FROM all_tab_columns WHERE table_name = '<TABLE_NAME>'
Microsoft SELECT * FROM information_schema.tables
SELECT * FROM information_schema.columns WHERE table_name = '<TABLE_NAME>'
PostgreSQL SELECT * FROM information_schema.tables
SELECT * FROM information_schema.columns WHERE table_name = '<TABLE_NAME>'
MySQL SELECT * FROM information_schema.tables
SELECT * FROM information_schema.columns WHERE table_name = '<TABLE_NAME>'

In non-Oracle databases, if you’re looking for user/application-created tables a helpful WHERE clause is table_schema='public'

SELECT * FROM information_schema.tables WHERE table_schema='public'

References

References