Question

I have two MySQL tables, and I want to find and replace text strings in one using data in another.

Table texts:

+---------------------+
|      messages       |
+---------------------+
| 'thx guys'          |
| 'i think u r great' |
| 'thx again'         |
| ' u rock'           |
+---------------------+

Table dictionary:

+--------------+---------------+
| bad_spelling | good_spelling |
+--------------+---------------+
|    'thx'     |    'thanks'   |
|    ' u '     |    ' you '    |
|    ' r '     |    ' are '    |
+--------------+---------------+

I want SQL to go through and look at every row in messages and replace every instance of bad_spelling with good_spelling, and to do this for all the pairs of bad_spelling and good_spelling.

The closest I have gotten is this:

update texts, dictionary
set texts.message = replace(texts.message,
                            dictionary.bad_spelling,
                            dictionary.good_spelling)

But this only changes “thx” to “thanks” (in two rows) and does not go on to replace ” u ” with ” you” or ” r ” with ” are .”

Any ideas how to make it use all the rows in dictionary in the replace statement?

---

PS forgot to mention that this is a small example and in the real thing I will have a lot of find/replace pairs, which may get added to over time.

Answer 1

I’ve never used MySql, so this is just a theory based on my other database work. When reading the other answers, trying to use REPLACE(), I thought I could post this and get someone with MySql syntax experience a few ideas to make a set base solution.

here is some SQL Server code to that does most of the work for you:

DECLARE @Source table (Texts varchar(50))
INSERT @Source VALUES ('thx guys')
INSERT @Source VALUES ('i think u r great')
INSERT @Source VALUES ('thx again')
INSERT @Source VALUES ('u rock')

DECLARE @Dictionary table (bad_spelling varchar(50), good_spelling varchar(50))
INSERT @Dictionary VALUES ('thx', 'thanks')
INSERT @Dictionary VALUES ('u', 'you')
INSERT @Dictionary VALUES ('r', 'are')

SELECT
    t.Texts,COALESCE(d.good_spelling,c.ListValue) AS WordToUse
    FROM @Source                                     t
        CROSS APPLY dbo.FN_ListToTable(' ',t.Texts)  c
        LEFT OUTER JOIN @Dictionary                  d ON c.ListValue=d.bad_spelling

OUTPUT:

Texts              WordToUse
------------------ ---------
thx guys           thanks
thx guys           guys
i think u r great  i
i think u r great  think
i think u r great  you
i think u r great  are
i think u r great  great
thx again          thanks
thx again          again
u rock             you
u rock             rock

(11 row(s) affected)

It would be better to use a “real” PK than the actual “Texts” in the query above, but the OP doesn’t list many columns in that table, so I use “Texts”.

Using SQL Server you need to use a some funky XML syntax to join the rows back together (so I won’t show that code, as it doesn’t matter), but using MySql’s GROUP_CONCAT() you should be able to concatenate the word rows back together into phrase rows.

the code for the (SQL Server) split function and how it works can be found here: SQL Server: Split operation