DELETE [FROM] {table_name|view_name} [WHERE clause] 在SQL SELECT 语句中可以使用的任何条件都可以在DELECT 语句的WHERE子句 中使用。例如,下面的这个DELETE语句只删除那些first_column字段的值为’goodbye’或second_column字段的值为’so long’的记录: 复制内容到剪贴板 代码: DELETE mytable WHERE first_col...
using index:只用到索引,可以避免访问表。 using where:使用到where来过虑数据。不是所有的where clause都要显示using where.。如以=方式访问索引。 using tmporary:用到临时表。 using filesort:用到额外的排序.。(当使用order by v1,而没用到索引时,就会使用额外的排序)。 range checked for eache record(...
-- Show the subject, the time that the mail item row was last-- modified, and the log information.-- Join sysmail_faileditems to sysmail_event_log-- on the mailitem_id column.-- In the WHERE clause list items where danw was in the recipients,-- copy_recipients, or blind_copy_recip...
There are different types of SQL constraints to aim for the accuracy and consistency of data in a table. Here are some common types of constraints, where we will clarify your understanding of SQL constraint syntax and examples: 1.NOT NULLConstraint The NOT NULL constraint means a column cannot...
ERRCODE_NOT_NULL_VIOLATION或者not-null constraint或者UsageProblem 报错:null value in column "xxx" violates not-null constraint 问题原因:违反非空约束,NOT NULL的列写入了NULL值。 解决方法:去掉NULL的脏数据后再进行写入。 ERRCODE_UNDEFINED_TABLE
ERRCODE_NOT_NULL_VIOLATION或者not-null constraint或者UsageProblem 报错:null value in column "xxx" violates not-null constraint 问题原因:违反非空约束,NOT NULL的列写入了NULL值。 解决方法:去掉NULL的脏数据后再进行写入。 ERRCODE_UNDEFINED_TABLE
SQL - WHERE Clause - The SQL WHERE clause is used to filter the results obtained by the DML statements such as SELECT, UPDATE and DELETE etc. We can retrieve the data from a single table or multiple tables(after join operation) using the WHERE clause.
ON clause回答1They are not the same thing. Consider these queries: SELECT * FROM Orders LEFT JOIN OrderLines ON OrderLines.OrderID=Orders.ID WHERE Orders.ID = 12345 and SELECT * FROM Orders LEFT JOIN OrderLines ON OrderLines.OrderID=Orders.ID AND Orders.ID = 12345 The first will return...
##三值逻辑,因为''等价与null,null跟任何非null的值比较都等于false SQL> select * from test where name=''; no rows selected SQL> select * from test where name=' '; --符号中' '有一个空格 ID NAME --- --- 3 1 row selected. SQL> select...
Null values generally indicate data that is unknown, not applicable, or to be added later. For example, a customer's middle initial might not be known at the time the customer places an order. Consider: To test for null values in a query, useIS NULLorIS NOT NULLin theWHEREclause. ...