下面看看原始SQL和增加DISTINCT后的差别: SQL> SET AUTOT TRACE SQL> SELECT T1.OBJECT_NAME, T1.OBJECT_TYPE,T2.TABLESPACE_NAME 2 FROM T1, T2 WHERE T1.OBJECT_NAME = T2.SEGMENT_NAMEAND T1.OBJECT_NAME IN 3 (SELECT INDEX_NAME FROM T3 WHERE T3.TABLESPACE_NAME= T2.TABLESPACE_NAME); 311 rows...
If you omit theDISTINCTkeyword, the SQL statement returns the "Country" value from all the records of the "Customers" table: Example SELECTCountryFROMCustomers; Try it Yourself » Count Distinct By using theDISTINCTkeyword in a function calledCOUNT, we can return the number of different countri...
以前也经常发现由于开发人员对SQL不是很理解,在SELECT列表的20多个字段前面添加了DISTINCT,造成查询的执行异常缓慢,基本上很难在ORA-1555错误出现之前得到查询的结果,甚至有些SQL会产生ORA-7445错误。所以在给开发人员培训的时候还着重介绍了一下DISTINCT的功能以及不正确地使用DISTINCT所带来的性能方面的负面影响。 不过这...
Here, the SQL command selects unique ages and orders them in descending order from theCustomerstable. To learn more, visitSQL ORDER BY. SELECT DISTINCT vs SELECT TheSELECT DISTINCTstatement is used when you want to return only unique (distinct) values in the result set. Whereas, a regularSEL...
DISTINCT is a clause used in SQL queries to eliminate duplicate rows from the result set. It is used along with the SELECT statement to identify unique values in a specific column or multiple columns of a table. The DISTINCT keyword ensures that only distinct or unique values are returned in...
If you want to select a list of all unique colors from all rows in the table, you can accomplish it by using the following SQL statement: SELECT DISTINCT Color FROM Cars; The DISTINCT keyword goes right away after the SELECT keyword, and in turn is followed by the column(s) we are se...
not exists:与exists相反,括号内子查询sql语句返回结果为空(即:sql不返回的结果为真),子查询的结果为空则条件成立,执行主slq,否则不执行。 总结:exists 和not exists语句强调是否返回结果集,不要求知道返回什么,与in的区别就是,in只能返回一个字段值,exists允许返回多个字段 提醒:文章中提供了exists和not exists的...
4ANDT1.OBJECT_NAMEIN 5( 6SELECTINDEX_NAMEFROMT3 7WHERET3.TABLESPACE_NAME=T2.TABLESPACE_NAME 8); 311rows selected. ExecutionPlan --- 0SELECTSTATEMENT Optimizer=CHOOSE (Cost=12Card=668Bytes=62124) 10HASHJOIN(SEMI) (Cost=12Card=668Bytes=62124) 21HASHJOIN(Cost=9Card=668Bytes=39412...
～+名词 distinct character 突出的性格 distinct honor 特 殊的荣誉 d istinct statement 明确声明 distinct view 清晰的景色 副词+～ quite distinct 全然不同 ～+介词 distinct from 和…不同 things distinct in kind 性质不同的东西 同义词辨析: SQL中Count和Distinct的使用 SQL中Count和Distinct的使⽤ 先来...
SQL DISTINCT Select with distinct Redundancy is the repetition of certain data in a table. With the use ofDISTINCTclause data redundancy may be avoided. This clause will eliminate the repetitive appearance of same data.DISTINCTcan come only once in a given select statement....