SELECT COUNT(*) AS count_asterisk, COUNT(1) AS count_1 FROM orders; Here's the result: count_asteriskcount_1 8 8 Both versions return the same number of rows. There’s a popular misconception that “1” in COUNT(1) means “count the values in the first column and return the numbe...
Wrapping COUNT in ISNULL means any overflow error will be silently suppressed, which should be considered for correctness. Examples A. Use COUNT and DISTINCT This example returns the number of different titles that an Adventure Works Cycles employee can hold. SQL Copy SELECT COUNT(DISTINCT Title...
When bothARITHABORTandANSI_WARNINGSareON, you can safely wrapCOUNTcall-sites inISNULL( <count-expr>, 0 )to coerce the expression's type toint NOT NULLinstead ofint NULL. WrappingCOUNTinISNULLmeans any overflow error will be silently suppressed, which should be considered for correctness. ...
p_sqlid IN VARCHAR2 ) AUTHID CURRENT_USER IS l_theCursor NUMBER; col_cnt NUMBER; col_rec dbms_sql.desc_tab; col_value VARCHAR2(4000); ret_val NUMBER; BEGIN l_theCursor := dbms_sql.open_cursor; dbms_sql.parse(l_theCursor, 'select sql.sql_text, cur.* from v$sql_shared_cursor c...
【测试类型:SQL功能】 3.0.1 从库COUNT结果与主库不一致,与SELECT 返回条数不一致 M【测试版本:3.0.1 】 问题描述【测试环境】单机/1主x备x级联备: 1主3从【版本及...
I need to know what COUNT DISTINCT means inSQL Server. What is the difference between COUNT and COUNT DISTINCT? How does it handle NULL values? Are there performance concerns when using COUNT DISTINCT in a SQL database? Solution COUNT is an aggregate function used inT-SQL codeto count the ...
(1)UNBOUND_CURSOR Theexisting child cursor was not fully built (in other words, it was notoptimized) (2)SQL_TYPE_MISMATCH The SQL type does not match the existing childcursor (3)OPTIMIZER_MISMATCH Theoptimizer environment does not match the existing child cursor. ...
sqlalchemy 多对多关系 sql多对多关联 1 一对多、多对多、自关联多对多、自关联一对多场景描述之前在做网页开发的时候一直用Sqlalchemy来操作数据库,当我用到自关联多对多和自关联一对多的时候,sqlalchemy的配置会有一些辅助的参数,配置起来很麻烦,灵机一动我就想了一下,为什么不能直接写sql呢!!!虽然sql语句写...
1 row in set (0.00 sec) 很明显出现问题的sql由于使用了count(item_id) ,而item_id字段并没有和 selid 和end_time 构成有效索引 故该sql 没有合理的使用索引 。查看其直系计划 root@db >explain select count(item_id) from xxxtable >where selid = 345705650 and end_time > now() \G ...
Background Currently, SQL Activity information is aggregated on an hourly basis. However, the latency percentiles that we record (p50, p90, p99) are aggregate separately as part of the insights infrastructure. This results in uncertain d...