The wording of the if not exists in MSSQL and SQLite

In the SQL name, if not exists is if not present, if exists is if present.

Below you learn the use of both.

A to determine if the database does not exist

Copy the code code as follows:
If not EXISTS (SELECT * from sys.databases WHERE name = ' database_name ')

b, when the judgment table does not exist

Copy the code code as follows:
If not EXISTS (SELECT * from sysobjects where id = object_id (' table_name ') and OBJECTPROPERTY (ID, ' isusertable ') = 1)

C, the Judgment column does not exist

Copy the code code as follows:
If not EXISTS (SELECT * from syscolumns where id=object_id (' table_name ') and Name= ' column_name ')

When the table is not saved, I can do the creation of the database, create the table, add columns, you can execute the corresponding SQL statements;

And if exists the same judgment, first of all to determine whether the query results exist, if there is execution judgment after the statement, query database, table, column method is the same;

MSSQL Syntax:

Copy the code code as follows:
If not exists (SELECT 1 from [t_table] where [fName] = ' Zhang San ')
INSERT into t_table values (' Zhang San ');

SQLite syntax:

Copy the code code as follows:
Insert INTO t_table select ' Zhang San '
Where NOT EXISTS (SELECT 1 from [t_table] where [fName] = ' Zhang San ');

The wording of the if not exists in MSSQL and SQLite