SQL if 语句语法错误

Question

I've been trying to write this simple mysql statement to check if a table exists:

IF object_id('carpool'.'users', 'U') is not null THEN
    PRINT 'Present!'
ELSE
    PRINT 'Not accounted for'
END IF

'carpool' is my schema and 'users' is a table My sql version is 5.1.52-community I keep getting this error:

Error Code: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF' at line 1   0.000 sec

I've tried several syntaxes such as IF BEGIN END ELSE BEGIN END to no avail. any ideas?

Answer 1

It looks like you're trying to do a form of T-SQL, which MySQL does not support.

There is no print function, nor object_id. There is a form of IF function that can be used in a SELECT statement:

SELECT IF(1 = 1, 'present', 'not');

Are you reading MSSQL doco instead of MySQL doco? MSSQL supports these functions.

Answer 2

Depending on what you are after, you might want to use something like this:

SELECT
  CASE WHEN EXISTS (SELECT NULL
                    FROM information_schema.tables 
                    WHERE table_schema = 'carpool' AND table_name = 'users')
       THEN 'Present'
       ELSE 'Not accounted for' END;

This will check if table users exists in carpool schema. Please see example here .

Answer 3

Every statement must be terminated by semicolon.

Like this

IF object_id('carpool'.'users', 'U') is not null THEN
   PRINT 'Present!';
ELSE
   PRINT 'Not accounted for';
END IF;