-1

I have two tables with structure

Table1
------   
No | Name | IDNo | HouseNoBlock

Table2
------ 
IDNo | HouseNo | Block

I am trying to update the HouseNoBlock Column of first table with value joined by HouseNo/Block while comparing the IDNo . I was able to get the values using the query

SELECT CONCAT(table2.HouseNo,'/',table2.Block) 
FROM   table2 ,table1 
WHERE  table1.IDNo = table2.IDNo

but when I try to UPDATE table1 I am getting a Syntax error ERROR 1064 (42000) .

UPDATE table1 
SET    HouseNoBlock = CONCAT (table2.HouseNo,'/',table2.Block) 
FROM   table2 ,table1 
WHERE  table1.IDNo = table2.IDNo

Can somebody help with this?

2

Since you have not supplied any data, I've prepared next example:

create table tbl1 (No int, Name varchar(200), IDNo int, HouseNoBlock varchar(200));

create table tbl2 (IDNo int, HouseNo varchar(100), Block varchar(100));

insert into tbl1 values 
(1, 'Name1', 1, null), 
(2, 'Name2', 2, null), 
(3, 'Name3', 1, null);

insert into tbl2 values 
(1, 'House1', 'Block1'), 
(2, 'House2', 'Block2');

Use next sentence:

UPDATE tbl1  --< first the table that will be updated
JOIN   tbl2
ON     tbl1.IDNo = tbl2.IDNo
SET    HouseNoBlock = CONCAT(tbl2.HouseNo,'/',tbl2.Block);

This is final result:

No | Name  | IDNo | HouseNoBlock 
-: | :---- | ---: | :------------
 1 | Name1 |    1 | House1/Block1
 2 | Name2 |    2 | House2/Block2
 3 | Name3 |    1 | House1/Block1

dbfiddle here

Have a look at MySQL docs about UPDATE syntax:

UPDATE [LOW_PRIORITY] [IGNORE] table_reference
    SET assignment_list
    [WHERE where_condition]
    [ORDER BY ...]
    [LIMIT row_count]

For the multiple-table syntax, UPDATE updates rows in each table named in table_references that satisfy the conditions. Each matching row is updated once, even if it matches the conditions multiple times. For multiple-table syntax, ORDER BY and LIMIT cannot be used.

  • Can you please clarify on which table to use first on a comparison WHERE clause . – Anoop D Mar 23 '18 at 14:19
  • 1
    The table that will be updated. – McNets Mar 23 '18 at 14:20
  • My tbl1 is really large with some 18 billion rows and i need this join to be restricted using a WHERE condition on tbl1 at the end of query , but still it is traversing whole rows , will adding the WHERE condition to join with an AND will work . – Anoop D Mar 24 '18 at 7:47

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