MySql AND运算符针对单列（在一列的两行之间进行比较）

Question

I have been trying to execute this query but it's not working.

Would appreciate if anyone helps;

SELECT DISTINCT(fld_tech_id) 
FROM tbl_tech_properties 
WHERE fld_tech_category_value_id = 236 
    AND fld_tech_category_value_id = 234

Answer 1

It's impossible for your WHERE condition to ever match because it is tested for each row in the table and no single row can have fld_tech_category_value_id equal to both 234 and 236 at the same time. Instead you should group by fld_tech_id and check that your group contains two rows.

SELECT fld_tech_id
FROM tbl_tech_properties
WHERE fld_tech_category_value_id IN (234, 236)
GROUP BY fld_tech_id
HAVING COUNT(DISTINCT fld_tech_category_value_id) = 2

See it working online: sqlfiddle

Answer 2

Why don't you just use

 
 
 
 
  
  
  SELECT DISTINCT fld_tech_id FROM tbl_tech_properties WHERE fld_tech_category_value_id IN (236,234) ;
 
 
  

Results based on sample data on the reference:

sample table:

FLD_TECH_ID     FLD_TECH_CATEGORY_VALUE_ID
1               234
2               256
3               236
3               250
2               226
3               216
1               240
1               236

Results:

 
 
 
 
  
  
  FLD_TECH_ID 1 3
 
 
  

REFERENCE SQLFIDDLE

A solution that works:

SELECT DISTINCT fld_tech_id
FROM tbl_tech_properties AS t
WHERE EXISTS
      ( SELECT *
        FROM tbl_tech_properties AS t1
        WHERE t1.fld_tech_id = t.fld_tech_id
          AND t1.fld_tech_category_value_id = 236
      )
  AND EXISTS
      ( SELECT *
        FROM tbl_tech_properties AS t2
        WHERE t2.fld_tech_id = t.fld_tech_id
          AND t2.fld_tech_category_value_id = 234
      )  ;

Referernce SQL-Fiddle test 2