在Oracle数据库中,count(1)和count(*)都是用来计算表中记录数的聚合函数,但它们在实现上略有不同。 1. count(1):使用count(1)时,数据库会选择任意一列(通常是第一...
count(1)包括了忽略所有列,用1代表代码行,在统计结果的时候,不会忽略列值为NULL count(列名)只包括列名那一列,在统计结果的时候,会忽略列值为空,不统计列值为NULL 执行效率上 列名为主键,count(列名)会比count(1)快; 列名不为主键,count(1)会比count(列名)快 如果表多个列并且没有主键,则 count(1) 的...
原本的cql: select count(1) from keyspaceName.table_name; 完整的ssh command:sudo -u dean cqlsh 127.0.0.1 --ssl -u cassandra -ppassword -e 'use keyspaceName; select count(1) FROM table_name;' |grep -A2 count | xargs| awk '{print $NF}'这条命令会最终直接输出行数 修改后的cql:copy ...
0 Count function in Oracle 1 count query filter 2 Multiple Select statement using COUNT 1 oracle sql count multiple columns 0 Why does count(*) not return a single-group? 1 SQL - How to display only certain values of the Count Aggregate Function? 2 is it possible to put condition ...
select count(1) from student where 岁数 = '18'union all select count(1) from student where 岁数 = '19'这样得到的是两条数据各是一个字段 select a.c_1,b.c_2 from (select count(1) as c_1 from student where 岁数 = '18') a,(select count(1) as c_2 from student ...
The syntax for the COUNT function in Oracle/PLSQL is: SELECT COUNT(aggregate_expression) FROM tables [WHERE conditions]; OR the syntax for the COUNT function when grouping the results by one or more columns is: SELECT expression1, expression2, ... expression_n, ...
http://www.oracledba.co.uk/tips/count_speed.htm which shows (as Tom points out) that they all work the same nowadays... Hi, tom: Here is my test result, it show count(*) is much fast than count(1). In other condition ( for example, a query with join), sometime i can find...
In Oracle 11g, you can use: SELECT rw, grp, pdate, COUNT(*) OVER (PARTITION BY mn) AS cnt FROM ( SELECT rw, grp, pdate, SUM(has_changed) OVER (ORDER BY rw) AS mn FROM ( SELECT rw, grp, pdate, CASE LAG(grp) OVER (ORDER BY rw) WHEN grp THEN 0 ELSE ...
SQL COUNT(*) 语法 COUNT(*) 函数返回表中的记录数:SELECT COUNT(*) FROM table_name;SQL COUNT(DISTINCT column_name) 语法 COUNT(DISTINCT column_name) 函数返回指定列的不同值的数目:SELECT COUNT(DISTINCT column_name) FROM table_name;注释:COUNT(DISTINCT) 适用于 ORACLE 和 Microsoft SQL...
弄清楚COUNT(1)、COUNT(*)、COUNT(常量)、COUNT(主键)、COUNT(ROWID)、COUNT(非空列)、COUNT(允许为空列)、COUNT(DISTINCT 列名)之间的区别,以及它们之间的效率问题。 2.3实验过程 2.3.1实验脚本 --创建1W行的表 DROP TABLE T_COUNT_LHR; CREATE TABLE T_COUNT_LHR AS ...