H2 supports a syntax to safely drop constraint if it not exists i.e. drop constraint if exists fk_symbol. The similar syntax is used in MariaDB: drop foreign key if exists fk_symbol but the original ...

检查了后，发现表DAY_BOOK_REPORT确实不存在字段UNIT_PRICE_PCS，但是给表加字段时就报这个错误，遂咨询了一下他具体的操作过程 ...

-- The EXISTS operator is used to test for the existence of any record in a subquery. -- The EXISTS operator returns TRUE if the subquery returns one or more records. -- It can be used in a SELECT, ...

Dynamic PHP pages give you the option to choose a MySQL table dynamically from which to query. You must ensure that the table exists before running a query on the table. PHP has a quick function that ...