Does not matter for inner joins 【做inner join的时候没影响,但是做outer join的时候就会有影响】 Matters for outer joins a. WHERE clause: After joining. Records will be filtered after join has taken place. b. ON clause - Before joining. Records (from right table) will be filtered before jo...
A column contains alarge number of null values One or more columns arefrequently usedtogether in awhereclause or ajoincondition The table is large and most queries are expected toretrieve less than 2% to 4%of the rows in the table 不建议创建索引 The columns arenotoften used asa conditionin...
Exercise? What is the purpose of the SQL WHERE clause? To specify the table from which to select data To filter records that meet a specified condition To join multiple tables together To sort records in ascending orderSubmit Answer »Video: SQL WHERE Clause...
a.WHEREclause:Afterjoining. Records will be filtered after join has taken place. b.ONclause -Beforejoining. Records (from right table) will be filtered before joining. This may end up as null in the result (since OUTER join).
In theWHEREclause, specify the join condition. If the underlying fact table is partitioned, you must also specify one of thelocal_partitioned_indexclauses (seelocal_partitioned_index). Restrictions on bitmap join indexes:In addition to the restrictions on bitmap indexes in general (seeBITMAP)...
A WHERE clause can be added to a DELETE statement to only delete the rows that match a specific condition. For example, suppose we need to delete only the rows belonging to the employees (“EM”) from the Person table. In that case, we should use the following SQL command: ...
ON <search_condition>指定聯結所根據的條件。 條件可以指定任何述詞 (雖然通常都是使用資料行和比較運算子),例如:SQL 複製 SELECT p.ProductID, v.BusinessEntityID FROM Production.Product AS p INNER JOIN Purchasing.ProductVendor AS v ON (p.ProductID = v.ProductID); ...
JOIN指出所指定的聯結作業必須發生在所指定的資料表來源或檢視表之間。ON <search_condition>指定聯結所根據的條件。 條件可以指定任何述詞 (雖然通常都是使用資料行和比較運算子),例如:SQL 複製 SELECT p.ProductID, v.BusinessEntityID FROM Production.Product AS p INNER JOIN Purchasing.ProductVendor AS v ...
DELETE FROM FROM JOIN <another_table> ON <join_condition> WHERE <where_condition> TRUNCATE TABLE [/code] 以上3个语句: 第1个是SQL标准的删除语句(WHERE子句省略的结果是删除全部数据,注意!); 第2个是T-SQL扩展的删除语句,效果是将符合联接查询条件的目标表数据删除(将DELETE FROM 改为SELECT DISTINC...
Unlike theONclause, we use theWHEREclause to filter records after theJOINhas been performed. When we use theWHEREclause instead of theONclause toJOINthe tables, it functions as an implicitJOINcondition for anINNER JOIN. TheWHEREclause can introduce extra conditions to filter the result set, ena...