SQL
`IF NOT EXISTS`
The `IF NOT EXISTS` syntax will only proceed with the creation of the table if it does not already exist. If the table already exists, no action will be taken and the existing table will remain in the database.  
Create a table with two integer columns (` i` and `j`) only if `t1` does not exist yet:  
```sql
CREATE TABLE IF NOT EXISTS t1 (i INTEGER, j INTEGER);
```