Mysql将列分为3列以在phpMyAdmin中查看

Question

I'm extremely new to writing SQL queries - I am hoping to create some charts in a front end application, but have to manipulate the data to create a view because the front end is not well suited to running complicated queries.

Here is my current situation: I have a table that has client data as well as a date that record was created. Here is a sample not in any particular order.

|  ID  |   post_date   |    post_title    |
-------------------------------------------
| 1654 |  2017-09-04   | Bill Smith (5678)|
| 1658 |  2017-09-05   | Jan Jones (3423) |
| 1878 |  2017-08-17   | Jim Tanz (7890)  |
| 1659 |  2017-09-06   | Jan Jones (3425) |

I would like to display unique values by last name, but at the moment all the names are in one column. The ID is unique as it is incremented for each record and the number in parentheses (transaction ID) appended to the last name is also unique and comes from another application we are pulling the name from.

I have been able to split the post_title column, but only into 2 columns but am left with FName and LastName (TrID), which doesn't allow me to pick distinct entries by last name to do a client count because the TrIDs are all different.

My intent was to create a view with 3 columns then display distinct entries by last name and count the clients, each month to see if there has been any client growth, but I am still at the very early step.

Any assistance would be greatly appreciated (and remembered forever :>) Thanks!

Answer 1

Some text operations and it may work:

SELECT t.post_title
      ,LEFT(t.post_title, LOCATE(' ', post_title )) AS FName
      ,SUBSTR(t.post_title, LOCATE(' ', post_title)+1, LOCATE(' ',post_title,LOCATE(' ', post_title)+1)-LOCATE(' ', post_title)) AS LName
      ,REPLACE(REPLACE(TRIM(RIGHT(t.post_title,LOCATE(' ', REVERSE(post_title)))), '(', ''), ')','') AS ID
FROM (SELECT 'Bill Smith (5678)' AS post_title
      UNION SELECT 'Jan Jones (3423)'
      UNION SELECT 'Jim Tanz (7890)') t;

Rextester Demo

Answer 2

You can use SUBSTRING_INDEX to separate the string, so to retrieve the first name:

SUBSTRING_INDEX(post_title," ",1)

This gets everything up until the nth instance of the space, so it's a bit messier to get the last name, as when using '2' we will get the values up until the second space, then we need to then extract the second value (-1, as we go backwards). Therefore, getting the 'Last Name' is done using:

SUBSTRING_INDEX(SUBSTRING_INDEX(post_title," ",2)," ",-1)

Scenario 1: Splitting post_title into three fields:

SELECT
SUBSTRING_INDEX(post_title," ",1) as firstName, 
SUBSTRING_INDEX(SUBSTRING_INDEX(post_title," ",2)," ",-1) as lastName,
SUBSTRING_INDEX(REPLACE(REPLACE(post_title,"(",""),")","")," ",-1) as post_ID
FROM tableName;

Output:

+-----------+----------+---------+
| firstName | lastName | post_ID | 
---------------------------------+
| Bill      | Smith    | 5678    | 
| Jan       | Jones    | 3423    | 
| Jim       | Tanz     | 7890    | 
| Jan       | Jones    | 3425    | 
+-----------+----------+---------+

Scenario 2: Grouping functions

You could also use the named field to group and count by Last Name

SELECT
COUNT(*) as Qty,
SUBSTRING_INDEX(SUBSTRING_INDEX(post_title," ",2)," ",-1) as lastName
FROM tableName
GROUP BY lastName;

Output:

+-----+----------+
| Qty | lastName |
+-----+----------+
|  2  | Jones    |
|  1  | Smith    | 
|  1  | Tanz     |
+-----+----------+

And so on. Hard to tailor this any further, as I'm not fully sure what you're intending to do, but hopefully the above is of use.