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...
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...
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 ...
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. ...
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)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. ...
【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 【版本及同步状态】 zdhdb=# select * from dbe_perf.global_recovery_status;node_name | standby_node_name | source_ip | ...
into the zero value forLatencyInfowhich means that thecurrent execution's latency is assumed to be the max. We then use that latency to clamp the percentiles down if they happen to be higher,which they will be if any prior execution contained higher latencies. This is done in theAddmethod....
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 ...
OpenCV中K-means源码解析 = DBL_MAX, compactness = 0;//DBL_MAX,64位浮点数最大取值 RNG& rng = theRNG();//Returns the default random...*= criteria.epsilon; if( criteria.type & TermCriteria::COUNT )//最大迭代次数 criteria.maxCount...i个元素中内容:[所有特征向量中第i维的最小值,特征向量...