In MySQL it is pretty easy to drop a table if it exists already. In Oracle and Microsoft’s SQL Server it is a little more complicated. Today I want to present you the solutions for these two DBMS’. MySQL: DROP TABLE IF EXISTS [table_name] Oracle: BEGIN EXECUTE IMMEDIATE 'DROP TABLE...
For example, the following statement attempts to drop the purchase_orders table that does not exist: DROP TABLE IF EXISTS purcchase_orders;Code language: PostgreSQL SQL dialect and PL/pgSQL (pgsql) Dropping tables with constraints First, create two new tables called brands and cars: CREATE TA...
DROP TABLE IF EXISTS [table_name] Oracle: BEGIN EXECUTE IMMEDIATE 'DROP TABLE [table_name]'; EXCEPTION WHEN OTHERS THEN NULL;END; SQL Server: IF EXISTS ( SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = '[table_name]')DROP TABLE [table_name]...
select 'select '||'''||table_name ||''','||'count(*) from '||table_name from user_all_tables ; 把上面这段sql的执行结果拷贝出来执行即可 36. SQLPLUS里执行EXPLAIN PLAN SQL>EXPLAIN PLAN FOR你的sql语句; 如 SQL>EXPLAIN PLAN FOR SELECT * FROM EMP WHERE EMPNO=7369; 然后 SELECT plan_ta...
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Let's look at an example of how to use the TRUNCATE TABLE statement in Oracle/PLSQL. For example: TRUNCATE TABLE customers; This example would truncate the table called customers and remove all records from that table. It would be equivalent to the following DELETE statement in Oracle: DELETE...
The PL/SQL block inExample 6-9increases the salary for employees whose manager's ID number is 7902, 7698, or 7839, with and without bulk binds. Without bulk bind, PL/SQL sends a SQL statement to the SQL engine for each updated employee, leading to context switches that slow performance....
SQL macros and the WITH clause Leave a reply SQL macros and WITH clause are not known to be great friends: you cannot call a SQL macro in a WITH clause and if you want to define a table macro returning a query containing a WITH subquery(ies), then you won’t be able to use scalar...
&sql.TxOptions{Isolation: sql.LevelDefault, ReadOnly: false}),如果txOptions为nil,使用zorm.DataSourceConfig.DefaultTxOptions _, err := zorm.Transaction(ctx, func(ctx context.Context) (interface{}, error) { // 创建一个EntityMap,需要传入表名 entityMap := zorm.NewEntityMap(demoStructTableName...
SQL> The following example shows how to change the user interface language in SQLcl to French (fr), and also increase the maximum memory available to SQLcl (-Xmx800m): Copy c:\SQLDev\sqlcl\20.2\sqlcl\bin>SET JAVA_TOOL_OPTIONS=-Duser.language=fr -Xmx800m c:\SQLDev\sqlcl\20.2\sql...