Single SQL SELECT Returning multiple rows from one table row

问题

We have a table which is of the form:

ID,Value1,Value2,Value3
1,2,3,4

We need to transform this into.

ID,Name,Value
1,'Value1',2
1,'Value2',3
1,'Value3',4

Is there a clever way of doing this in one SELECT statement (i.e without UNIONs)? The column names Value1,Value2 and Value3 are fixed and constant.

The database is oracle 9i.

回答1:

This works on Oracle 10g:

select id, 'Value' || n as name,
       case n when 1 then value1 when 2 then value2 when 3 then value3 end as value
from (select rownum n
      from (select 1 from dual connect by level <= 3)) ofs, t

I think Oracle 9i had recursive queries? Anyway, I'm pretty sure it has CASE support, so even if it doesn't have recursive queries, you can just do "(select 1 from dual union all select 2 from dual union all select 3 from dual) ofs" instead. Abusing recursive queries is a bit more general- for Oracle. (Using unions to generate rows is portable to other DBs, though)

回答2:

Give a union a shot.

select ID, 'Value1' as Name, Value1 as Value from table_name union all
select ID, 'Value2', Value2 as Value from table_name union all
select ID, 'Value3', Value3 as Value from table_name

order by ID, Name

using union all means that the server won't perform a distinct (which is implicit in union operations). It shouldn't make any difference with the data (since your ID's should HOPEFULLY be different), but it might speed it up a bit.

回答3:

You can do it like this, but it's not pretty:

SELECT id,'Value 1' AS name,value1 AS value FROM mytable
UNION
SELECT id,'Value 2' AS name,value2 AS value FROM mytable
UNION
SELECT id,'Value 3' AS name,value3 AS value FROM mytable

回答4:

Unioning three select statements should do the trick:

SELECT ID, 'Value1', Value1 AS Value
FROM TABLE
UNION
SELECT ID, 'Value2', Value2 AS Value
FROM TABLE
UNION
SELECT ID, 'Value3', Value3 AS Value
FROM TABLE

回答5:

If you're using SQL Server 2005+ then you can use UNPIVOT

CREATE TABLE #tmp ( ID int, Value1 int, Value2 int, Value3 int)

INSERT INTO #tmp (ID, Value1, Value2, Value3) VALUES (1, 2, 3, 4)

SELECT
    *
FROM
    #tmp

SELECT
    *
FROM
    #tmp
UNPIVOT
(
    [Value] FOR [Name] IN (Value1, Value2, Value3)
) uPIVOT

DROP TABLE #tmp

回答6:

A UNION ALL, as others have suggested, is probably your best bet in SQL. You might also want to consider handling this in the front end depending on what your specific requirements are.

回答7:

CTE syntax may be different for Oracle (I ran it in Teradata), but I only used CTE to provide test data, those 1 2 3 and 4. You can use temp table instead. The actual select statement is plain vanilla SQL and it will on any relational database.

回答8:

For Sql Server, consider UNPIVOT as an alternative to UNION:

SELECT id, value, colname
FROM #temp t
UNPIVOT (Value FOR ColName IN (value1,value2,value3)) as X

This will return the column name as well. I'm unsure what the X is used for, but you can't leave it out.

回答9:

Try this:

CTE creates a temp table with 4 values. You can run this as is in any database.

with TEST_CTE (ID) as

(select * from (select '1' as a) as aa  union all
select * from (select '2' as b) as bb  union all
select * from (select '3' as c) as cc  union all
select * from (select '4' as d) as dd )

select a.ID, 'Value'|| a.ID, b.ID
from TEST_CTE a, TEST_CTE b
where b.ID = (select min(c.ID) from TEST_CTE c where c.ID > a.ID)

Here is the result set:

1   Value1  2

2   Value2  3

3   Value3  4

Enjoy!

Some afterthoughts.

^^^ CTE syntax may be different in Oracle. I could only run it in Teradata. You can substitute it with temp table or fix the syntax to make it Oracle compatible. The select statement is plain vanilla SQL that will work on any database.

^^^ Another thing to note. If ID field is numeric, you might need to cast it into CHAR in order to concatenate it with "Value".

来源：https://stackoverflow.com/questions/887870/single-sql-select-returning-multiple-rows-from-one-table-row

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