We might have a requirement to replace NULL values with a particular value while viewing the records. We do not want to update values in the table. We can do this usingSQL ISNULL Function. Let’s explore this in the upcoming section. 在查看记录时,我们可能需要用特定值替换NULL值。 我们不...
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(...
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...
SQL DeleteSQL Where can use "case when" in where clause SQL Order By can use "case when" in order by clause SQL Group BySQL AND & ORSQL LikeSQL COUNT distinctSQL InSQL BetweenSQL AliasesSQL Not NullSQL(ES) DateSQL avg()SQL count()SQL last()...
Select customername, contactname, address from customers where address is not null Update statement modify the existing records in a table UPDATE table_name SET column1 = value1, column2 = value2, … WHERE condition; The WHERE clause specifieswhich record(s) that should be updated. If you ...
3-WHERE clause 子句 4-AND OR NOT operators 运算符 5-IN operator 运算符 6-BETWEEN operator 运算符 / BETWEEN … AND … 7-LIKE operator 运算符 模糊搜索 8-REGEXP operator 运算符 9-IS NULL operator 运算符 / 如何搜索缺失了属性的记录 10-ORDER BY clause 子句 / 为数据排序 11-LIMIT clause ...
Alter_clause分为partition、rollup、schema change和rename四种。 partition支持的操作 增加分区 语法: ADD PARTITION [IF NOT EXISTS] partition_name VALUES LESS THAN [MAXVALUE|("value1")] ["key"="value"] [DISTRIBUTED BY RANDOM [BUCKETS num] | DISTRIBUTED BY HASH (k1[,k2 ...]) [BUCKETS num]...
希望选取NULL记录时,需要在条件表达式中使用IS NULL运算符。希望选取不是NULL的记录时,需要在条件表达式中使用IS NOT NULL运算符。 相关代码如下: -- SQL语句中也可以使用运算表达式 SELECT product_name, sale_price, sale_price * 2 AS "sale_price x2" FROM product; -- WHERE子句的条件表达式中也可以使用...
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. ...