Table Structure

This table is called Postcode_tbl:

INSERT SELECT Query Example

Let’s assume we have a table with the exact same structure as Postcode_tbl, but it’s called Postcode_tbl_2, and we want to copy all the rows from Postcode_tbl into Postcode_tbl_2 where the first 2 characters of the postcode is “CM”.

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INSERT INTO
Postcode_tbl_2
(
postcode,
longitude,
latitude
)
SELECT
postcode,
longitude,
latitude
FROM
Postcode_tbl
WHERE
postcode LIKE 'CM%'

Now, the table structure DOESN’T need to be the same in order to use a INSERT SELECT query. I just used the same structure for ease. If the table structure differs, or the field names don’t match, just make sure you specify the correct field names and order of fields in your query.

Example 1: Removing rows with a specific duplicate field:

As you can see, the field “postcode” has duplicated rows.

STEP 1: Copy table structure

I used the following code to duplicate the table structure of `postcodes` (if you use PhpMyAdmin, you can use the shortcuts):

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CREATE TABLE `DB_NAME`.`postcodes2` (
`postcodenospace` varchar( 10 ) NOT NULL ,
`longitude` varchar( 15 ) NOT NULL ,
`latitude` varchar( 15 ) NOT NULL
)

STEP 2: run query:

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INSERT INTO
postcodes2
(
postcode,
longitude,
latitude
)
SELECT postcode,longitude,latitude
FROM `postcodes` 
GROUP BY postcode

That’s it. All the rows with a unique postcode will get inserted into the table “postcodes2″.

The result

The key is in the SELECT query, where the postcode field is grouped together. That effectively puts all the duplicate postcodes together, generating a result of rows with unique postcodes.

Example 2: Removing duplicate rows:

STEP 1: Copy table structure

Use the code above to copy the table structure.

This example is slightly different, look at the data:

The previous example simply filtered the data by duplicate postcodes. As you can see, the highlighted row has different longitude and latitude values. So if you want to filter the data by unique rows, you need the following query:

STEP 2: Run the query

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INSERT INTO
postcodes2
(
postcode,
longitude,
latitude
)
SELECT postcode,longitude,latitude
FROM `postcodes` 
GROUP BY concat(postcode,longitude,latitude)

The result

Again, the key is the SELECT query. This time the query groups all the fields together (using the CONCAT function), to return rows with completely unique values.

The question is:

How do you count how many images there are in the images column for the entire table?

From what I’m aware, you can’t do it with a standard MySQL function. So the solution? You have to create your own function. The function needs to count how many times “.jpg” is present in the “image” column.

Solution: Step 1- Create the Function

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CREATE FUNCTION substrCount(x varchar(255), delim varchar(12)) returns int
return (length(x)-length(REPLACE(x,delim, '')))/length(delim);

Run the above query to create your MySQL function.

Solution: Step 2- Run the query with your new function

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SELECT SUM(substrCount(images,'.jpg')) from TABLE

Run that query and you’ll get the total times “.jpg” occurs in the ‘images’ column, consequently giving you a total count of how many images there are.

Notes

The MySQL function you created (substrCount) will remain stored in your DB until it is manually dropped, so you won’t need to create it again- you can call it whenever you want.