select *from customerswhere address like ‘%Trail%’ oraddress like ‘%avenue%’LIKE 执行优先级在逻辑运算符之后,毕竟 IN BETWEEN LIKE 本质可看作是比较运算符的简化,应该和比较运算同级,数学→比较→逻辑,始终记住这个顺序,上面这个如果用正则表达式会简单得多 where phone like ‘%9’/where phonenot like...
SQL_MAX_COLUMNS_IN_INDEX 2.0 一个SQLUSMALLINT 值,该值指定索引中允许的最大列数。 如果没有指定的限制或限制未知,则此值设置为零。 SQL_MAX_COLUMNS_IN_ORDER_BY 2.0 一个SQLUSMALLINT 值,该值指定 ORDER BY 子句中允许的最大列数。 如果没有指定的限制或限制未知,则此值设置为零。符合FIPS 入口级别...
WHERE条件句或者是HAVING条件句"condition":"WHERE",// 优化前的原始语句"original_condition":"(`config`.`id` = 1)","steps":[{// 转换类型句"transformation":"equality_propagation",//转换之后的结果输出"resulting_condition":"multiple equal(1, `config`.`id`)"},{"transformation":"constant_propaga...
If a table appears only in a subquery and not in the outer query, then columns from that table can't be included in the output (the select list of the outer query). Statements that include a subquery usually take one of these formats: WHERE expression [NOT] IN (subquery) WHERE expressi...
Single row subquery : Returns a single row of values. Multiple row subquery : Returns one or more rows. Table Subquery: Returns a result set that can be treated as a table Correlated subqueries : Reference one or more columns in the outer SQL statement. The subquery is known as a correlat...
Query hints can be specified only in the top-level query, not in subqueries. When a table hint is specified as a query hint, the hint can be specified in the top-level query or in a subquery. However, the value specified...
mysql> select distinct tiny_column from big_table limit 2; mysql> -- Returns the unique combinations of values from multiple columns. mysql> select distinct tiny_column, int_column from big_table limit 2; distinct可以和聚合函数(通常是count函数)一同使用,count(disitnct)用于计算出一个列或多个...
4.How does the COUNT() function interact with DISTINCT on multiple columns? The COUNT() function can be used with a subquery containing DISTINCT to count the number of unique rows based on the specified columns. 5.What happens if we use DISTINCT on all columns of a table?
Inserting data into view is valid only when we need to allow inserting data into specific columns without allowing users to insert into all columns in the destination table. Inserting data from a subquery into a table Subqueries are another option to insert multiple rows in SQL. They can be...
check for the existence of multiple columns in a table Check for valid Ip address Check if amount is positive or negative Check If Column Is PRIMARY KEY Check if database exists? Check if Feb-29 is falling between start and end dates Check if file exists then delete it- fix code Check ...