importcom.alibaba.druid.sql.SQLUtils;importcom.alibaba.druid.sql.ast.SQLObject;importcom.alibaba.druid.sql.ast.SQLStatement;importcom.alibaba.druid.sql.ast.statement.*;importcom.alibaba.druid.sql.dialect.hive.visitor.HiveSchemaStatVisitor;importjava.util.List;publicclassDruidTest{publicstatic void main(...
………//获得MyBatis框架生成的UserMapper接口的实现类UserMapperuserMapper=sqlSession.getMapper(UserMapper...
CASE Statement on multiple columns CASE STATEMENT RETURNING MULTIPLE ROWS Case Statement returning multiple values CASE statement returns "Invalid Column Name" Error Case statement that increments variable with 1 is giving error Case Statement using Divide CASE Statement when not null , else if Help Ca...
CASE WHEN is like an IF statement in a programming language. It is useful when we need to calculate a statistic on a certain subset of the data. In the image above, I calculate an average price for products sold in the US. I wasn’t careful with the ELSE in the CASE WHEN. In the...
最左前缀匹配原则,mysql会一直向右匹配直到遇到范围查询(>、<、between、like)就停止匹配,比如 a=1 and b=2 and c>3 and d=4 ,如果建立了(a,b,c,d)顺序的索引,d是用不到索引的,如果建立(a,b,d,c)的索引则都可以用到,a、b、d的顺序可以任意调整。
CREATETABLEempty_key_value_storeLIKEkey_value_store; 定义数据倾斜字段和值 使用SKEWED BY 语法来指定表中某些字段的倾斜值,以提高表的查询性能 代码语言:javascript 代码运行次数:0 运行 AI代码解释 CREATETABLElist_bucket_multiple(col1STRING,col2 int,col3STRING)SKEWEDBY(col1,col2)ON(('s1',1),('s3...
select*fromtable1wherenot(column1like'%value1%'orcolumn1like'%value2%'orcolumn1like'%value3%'); What happens if you don’t put those parenthesis in? Here are a few other posts you might enjoy: SQL Wildcards|SQL Multiple Filter|How to use the SQL In Statement with Subquery ...
mysql> SHOW STATUS LIKE ‘[匹配模式]’; ( 可以使用%、?等 ) 1. 2.优化参数 参数优化基于一个前提,就是在我们的数据库中通常都使用InnoDB表,而不使用MyISAM表。在优化MySQL时,有两个配置参数是最重要的,即table_cache和key_buffer_size。 table_cache ...
SQL_INSERT_STATEMENT SQL_INTEGRITY SQL_KEYWORDS SQL_LIKE_ESCAPE_CLAUSE SQL_NON_NULLABLE_COLUMNS SQL_OJ_CAPABILITIES SQL_ORDER_BY_COLUMNS_IN_SELECT SQL_OUTER_JOINS SQL_PROCEDURES SQL_QUOTED_IDENTIFIER_CASE SQL_SCHEMA_USAGE SQL_SPECIAL_CHARACTERS SQL_SQL_CONFORMANCE SQL_SUBQUERIES SQL_UNION SQL 限制 ...
This behavior is different from using parameters with default values in stored procedures in which omitting the parameter also implies the default value. However, the DEFAULT keyword isn't required when invoking a scalar function by using the EXECUTE statement. READONLY Indicates that the parameter ...