In this tutorial, we’ll discuss various methods to efficiently count distinct values, with the appropriate examples. 2. Simple SQL Query for Unique Values Counting unique values in a SQL column is straightforw
In SQL, theCOUNT()function is used to count the number of rows that match a specified condition. The DISTINCT keyword is used to return only distinct (unique) values. When combined, COUNT and DISTINCT can be used to count the number of unique values in a column or a set of columns. T...
//演示代码中非直接sql模式设置条件模式进行记录修改 public Long updateByQuery() { return lightDao.updateByQuery(StaffInfoVO.class, EntityUpdate.create().set("createBy", "S0001") .where("staffName like ?").values("张")); } //代码中非直接sql模式设置条件模式进行记录删除 lightDao.deleteByQuery...
SELECTCategory,COUNT(*)ASTotalProducts,SUM(CASEWHENPrice>100THEN1ELSE0END)ASExpensiveProductsFROM...
25、primary key:用法跟unique一样,区别是每个表可以多个unique,但是只能一个primary key。 26、foreign key:一个表中的foreign key 指向另外一个表的primary key;约束用于预防破坏表之间的链接动作。 27、check:create table 表名称1(列名称1 数据类型 not null,列名称2 数据类型,...check(列名称1>0));约束...
INSERT INTO 表名称 VALUES (值1, 值2,...); insert into age_grade values (1, 'A', 5000, 8000), (2, 'B', 8001, 10000), (3, 'C', 10001, 15000); 查询2018年12月员工各基本工资级别的人数 select grade, count(*) from salary as s inner join wage_grade as g on s.basic between...
1 mysql> -- Returns the unique values from one column. 2 mysql> select distinct tiny_column from big_table limit 2; 3 mysql> -- Returns the unique combinations of values from multiple columns. 4 mysql> select distinct tiny_column, int_column from big_table limit 2; distinct可以和聚合函数...
other aggregate functions such as SUM or AVG, COUNT doesn’t care what the values are in the column(s)—caring only that the rows exist. However, it can be modified by using the DISTINCT keyword to return a value that coincides with the number of unique values in the column in question...
自SQL Server 2016 (13.x) 起,可以对列存储索引创建一个或多个非聚集行存储索引,并对基础列存储执行高效表查找。 其他选项也可供使用。 例如,可以通过在行存储表中使用 UNIQUE 约束来强制主键约束。 由于非唯一值无法插入到行存储表中,因此 SQL Server 无法将值插入列存储。
Identify number of unique values in a column: TypeSELECT COUNT(DISTINCTcolumn name)[Enter]FROMtable name; Number of records matching criteria: TypeSELECT COUNT(*)[Enter]FROMtable name[Enter]WHEREcolumn name<,=,or>number; Thequeryelement, an important part of Structured Query Language, retrieves ...