Построение запроса на основе имени столбца в другой таблице

Question

Я хочу построить динамический запрос на основе структуры, представленной в другой таблице.

Вот пример того, как я хочу построить запрос на основена таблице выше -

select tbl1.col1,tbl1.col2,
tbl2.t2col1,tbl2.t2col2,tbl2.t2col3,tbl2.t2col3,
tbl3.t3col1,tbl3.t3col2,tbl3.t3col3,tbl3.t3col4
from tbl1 
inner join tbl2 on tbl1.col1=tbl2.t2col1 and tbl1.col2=tbl2.t2col2
inner join tbl3 on tbl1.col1=tbl3.t3col1 and tbl1.col2 = tbl3.t2col2

Answer 1

1) Структура таблицы конфигурации

CREATE TABLE [dbo].[ConfigQuery](
       [TableName] [varchar](max) NULL, -- Hold the table Name
       [ColumnName] [varchar](max) NULL, -- Column Nam for the Table
       [JoinColumn] [varchar](500) NULL, -- Join Column for the current  table
[JoinTable] [varchar](500) NULL, -- Join table for the current table
       [JoinTblColumn] [varchar](500) NULL, -- Column name of Join table with respect to current table column
       [SiteName] [varchar](500) NULL, -- Site name 
       [RowId] [int] NULL, -- For the purpose of loop, as CURSOR not supported in SQL DATA WAREHOUSE
       [ColAlias] [varchar](5000) NULL – Alias name for the column
       )

2) Процедура сохранения для перемещения данных из внешней таблицы в промежуточную таблицу

CREATE PROCEDURE MoveDataFromExternalToStagingTable
@StagingTable varchar(8000),-- Staging Table name
@SiteName varchar(8000) -- Site Name e.g LGW, PRW
AS
BEGIN 

DECLARE @FILE_CNT INT = (SELECT count(*) from ConfigQuery where SiteName= @SiteName); -- Hold total no.of rows count
Declare @query varchar(8000) =''; -- Columns for the query
Declare @from_query varchar(8000) =''; -- From condtion for query

Declare @JoinQuery varchar(8000) =''; -- Join condition for query
Declare @whereCon varchar(8000) =''; -- Where condition for query
Declare @finalQuery varchar(8000) =''; -- Final query @query + @from_query + @JoinQuery + @whereCon
DECLARE @LOOP_CNT INT = 1; 
declare       @j int=0;



--  While loop replaces cursor 
WHILE @LOOP_CNT <= @FILE_CNT 
BEGIN 
DECLARE @v_TableName NVARCHAR(4000) = (SELECT TableName FROM ConfigQuery WHERE rowId = @LOOP_CNT); -- Hold the table name for current row id
DECLARE @v_ColumnName NVARCHAR(4000) = (SELECT ColumnName FROM ConfigQuery WHERE rowId = @LOOP_CNT);  -- Hold the column name for table of current  row id
DECLARE @v_JoinTable NVARCHAR(4000) = (SELECT JoinTable FROM ConfigQuery WHERE rowId = @LOOP_CNT);  -- Hold the join table name for table of current  row id
DECLARE @v_JoinColumn NVARCHAR(4000) = (SELECT JoinColumn FROM ConfigQuery WHERE rowId = @LOOP_CNT);  -- Hold the join column name for table of current  row id
DECLARE @v_JoinTblColumn NVARCHAR(4000) = (SELECT JoinTblColumn FROM ConfigQuery WHERE rowId = @LOOP_CNT); -- Hold the join table column name for table of current  row id
DECLARE @v_Alias NVARCHAR(4000) = (SELECT ColAlias FROM ConfigQuery WHERE rowId = @LOOP_CNT); -- Hold the alias name for column 

DECLARE @first_TableName NVARCHAR(4000) = (SELECT TableName FROM ConfigQuery WHERE rowId = 1);
if @LOOP_CNT != @FILE_CNT
BEGIN
IF @v_Alias != NULL OR @v_Alias != ''
       set @query += @v_TableName +'.'+@v_ColumnName +' AS '+@v_Alias +' , ';
ELSE
       set @query += @v_TableName +'.'+@v_ColumnName +' , ';
END
else
BEGIN
       IF @v_Alias != NULL OR @v_Alias != ''
              set @query += @v_TableName +'.'+@v_ColumnName +' AS '+@v_Alias;
       ELSE
              set @query += @v_TableName +'.'+@v_ColumnName;
END


if @LOOP_CNT=1
BEGIN
set @from_query += 'from '+@v_TableName;

END
else
BEGIN
DECLARE @prev_TableName NVARCHAR(4000) = (SELECT TableName FROM ConfigQuery WHERE rowId = @LOOP_CNT-1);


if(@prev_TableName = @v_TableName) 
       BEGIN


              if @v_JoinColumn != null or @v_JoinColumn != ''
              BEGIN 
               if @j=0
              begin
                           set @joinquery +=  @v_JoinTable+'.'+@v_JoinTblColumn+' = '+@v_TableName+'.'+@v_JoinColumn;
              set @j=1
              end
              else
              begin
                    set @joinquery += ' and ' + @v_JoinTable+'.'+@v_JoinTblColumn+' = '+@v_TableName+'.'+@v_JoinColumn;
              end
              END
END
ELSE
       BEGIN
set @joinquery += ' inner join '+ @v_TableName + ' on ';
set @j=0
if @v_JoinTblColumn != null
set @joinquery +=  @v_JoinTable+'.'+@v_JoinTblColumn+' = '+@v_TableName+'.'+@v_JoinColumn;
END

END

SET @LOOP_CNT +=1;
END

Print @query
Print @from_query 
Print @joinquery
set @finalQuery = 'Insert into '+ @StagingTable + ' select '+@query + @from_query + @JoinQuery

exec(@finalQuery) -- executes the final query

END
--------------

Exec MoveDataFromExternalToStagingTable @StagingTable =’ Stagingtable’),-- Staging Table name
      @SiteName =’LGW’

Оператор результата SP-

Insert into Stagingtable select tbl1.col1 AS Column1 , tbl1.col2 , tbl2.t2Col1 , tbl2.t2Col2 , tbl2.t2Col3 AS Column3 , tbl2.t2Col4 , tbl3.t3Col1 , tbl3.t3Col2 , tbl3.t3Col3 , tbl3.t3Col4
from tbl1
inner join tbl2 on tbl1.col1 = tbl2.t2Col1 and tbl1.col2 = tbl2.t2Col2 inner join tbl3 on tbl2.t2Col1 = tbl3.t3Col3 and tbl1.col1 = tbl3.t3Col1 and tbl1.col2 = tbl3.t3Col2

Answer 2

Подготовьте динамический оператор SQL, который должен быть сгенерирован из вашей таблицы на основе условий.

SELECT 'SELECT * FROM '+ tablename+
        ' INNER JOIN '+joinTable+ ' ON '....
FROM table