sql - What is the difference between JOIN and UNION? - Stack …
2009年5月25日 · The SQL JOIN clause is used to combine records from two or more tables in a database. A JOIN is a means for combining fields from two tables by using values common to each. The SQL UNION operator combines the result of two or more SELECT statements. Each SELECT statement within the UNION must have the same number of columns.
sql - What is the difference between UNION and UNION ALL
2008年9月8日 · The difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records. Union Result set is sorted in ascending order whereas UNION ALL Result set is not sorted. UNION performs a DISTINCT on its Result set so it will eliminate any duplicate rows.
SQL UNIONs that use the WITH statement - Stack Overflow
2011年3月21日 · 1. The WITH statement indicates that the query expressed within the AS clause is a Common Table Expression (CTE). If you're asking if you can write more than one query that uses a CTE, then the answer is no. The closest approximation would be creating an inline table-valued function. (The simple definition of an ordinary table-valued function ...
Sql Server union with If condition - Stack Overflow
2012年11月1日 · 5. Best way to put condition in Query is CASE statement . you can put any number of condition in query . CASE statement is used to put conditional filters in Query . For EX. DECLARE @tmpValue. SET @tmpValue = 0 -- it will be change. SELECT * FROM Animal WHERE AniActive = 1. UNION. SELECT * FROM Animal.
mysql - SELECT UNION as DISTINCT - Stack Overflow
2012年1月9日 · The reason for this is, SQL cannot guess which values of Value to leave for you—and which to drop. That's something you need to define by yourself. That's something you need to define by yourself. Try using GROUP BY to ensure ID is not repeated, and any aggregate (here MIN , as in your example it was the minimum that survived) to select a ...
sql - UNION with WHERE clause - Stack Overflow
2017年3月20日 · SELECT * FROM (SELECT colA, colB FROM tableA UNION SELECT colA, colB FROM tableB) as tableC WHERE tableC.colA > 1. If we're using a union that contains the same field name in 2 tables, then we need to give a name to the sub query as tableC (in above query). Finally, the WHERE condition should be WHERE tableC.colA > 1.
Using union and count(*) together in SQL query - Stack Overflow
2009年8月12日 · 11. If you have supporting indexes, and relatively high counts, something like this may be considerably faster than the solutions suggested: SELECT name, MAX(Rcount) + MAX(Acount) AS TotalCount. FROM (. SELECT name, COUNT(*) AS Rcount, 0 AS Acount. FROM Results GROUP BY name. UNION ALL.
WHERE statement after a UNION in SQL? - Stack Overflow
2011年3月27日 · You probably need to wrap the UNION in a sub- SELECT and apply the WHERE clause afterward: SELECT * FROM Table1 WHERE Field1 = Value1. UNION. SELECT * FROM Table2 WHERE Field1 = Value2. Basically, the UNION is looking for two complete SELECT statements to combine, and the WHERE clause is part of the SELECT statement.
SQL UNION two tables with different column names
2018年5月23日 · How do I union two tables where their are columns that have different names in the two tables. Table1 has the column name 'Measure'; the data that matches this in Table2 has the column name 'Metric'. I have tried the following but it returns zero results when I run the query: Tag your question with the database you are using.
How to order by with union in SQL? - Stack Overflow
This allows sorts (orders) within UNIONs. So using an idea from @BATabNabber to separate each half of the Union, and @Wodin of wrapping the whole thing in a select, I got: Select Id, Name, Age from. (. Select Id, Name, Age, 1 as Mainsort. , ROW_NUMBER() over (order by age) as RowNumber. From Student.