从mySQL列字符串值中提取数值

Question

I have a "person" column in a mySQL database that represents the age and weight of a person as a string separated by a comma.

Example: "24,175"

I want to be able to separate and extract those values and cast them as numbers.

Example: turn "24,175" to

24 as age
175 as weight

So that I can write a query similar to the following

SELECT person 
FROM TABLE
WHERE age>140 OR weight>1000

I want to be able to check for values that are not possible. ie age>140 OR weight >1000.

I cannot modify the table/environment I'm working with

I only have access to queries.

I'm thinking about solving it this way

find the index where the comma exists. CHARINDEX(',',person)

Split the string into substrings using LEFT , RIGHT, CAST and CHARINDEX(',',person)

Cast age substring and weight substring to numbers using CAST(age AS INT) CAST(weight AS INT)

SELECT person
FROM TABLE
WHERE CAST(LEFT(person,CHARINDEX(',',person) AS INT)>150 OR CAST(RIGHT(person,CHARINDEX(',',person) AS INT) >1000

If I did anything wrong please correct me. Are all the functions usable/supported by mySQL? (RIGHT, LEFT, CHARINDEX) Will this work?

Exception: Another value for this column could be "unknown". Will this cause errors if we're trying to check for the index of , if it doesn't exist in the string? Is there a way to include "unknown" cases in the result and have it output a message of "error, person not recognized"

Answer 1

SELECT person
FROM TABLE
WHERE CAST(LEFT(person,LOCATE(',',person) AS INTEGER)>150 OR CAST(RIGHT(person,(LOCATE(',',person)+1) AS INTEGER) >1000

Instead of Char index use LOCATE im MqSQL

Also note the CAST function

Answer 2

you can also split is with SUBSTR_INDEX like this:

MariaDB [yourschema]> SELECT * FROM spliit;
+----+--------+
| id | d      |
+----+--------+
|  1 | 24,175 |
+----+--------+
1 row in set (0.03 sec)



MariaDB [yourschema]> SELECT
    ->     SUBSTRING_INDEX(d, ',', 1) AS age
    ->   , SUBSTRING_INDEX(d, ',', -1) AS weight
    ->
    -> FROM spliit;
+------+--------+
| age  | weight |
+------+--------+
| 24   | 175    |
+------+--------+
1 row in set (0.00 sec)

MariaDB [yourschema]>

sample

yes, you can direct calculate with it in MySQL

MariaDB [yourschema]> SELECT
    ->     SUBSTRING_INDEX(d, ',', 1)  + 2 AS age
    ->   , SUBSTRING_INDEX(d, ',', 1)  * 12 AS `month`
    ->   , SUBSTRING_INDEX(d, ',', -1) + 3 AS weight
    -> FROM spliit;

+------+-------+--------+
| age  | month | weight |
+------+-------+--------+
|   26 |   288 |    178 |
+------+-------+--------+
1 row in set, 1 warning (0.03 sec)

MariaDB [yourschema]>

Answer 3

You can do this all in the where clause:

where substring_index(person, ',', 1) + 0 > 140 or
      substring_index(person, ',' -1) + 0 > 1000

Note that the + 0 does an silent conversion to integers. And, substring_index() is much more convenient than the functions in SQL Server.

You can readily incorporate this logic into a view:

create view v_table as
     select t.*,
            substring_index(person, ',', 1) + 0 as age,
            substring_index(person, ',' -1) + 0 as weight
     from table t;

If you want to filter out bad values within the view , you can use a MySQL extension and add:

having age > 140 or weight > 1000

after the from clause.

Answer 4

You also can use VIRTUAL PERSITENT COLUMNS that calculate the fields automatis and you can also use a INDEX on each substr / Integer.

sample

MariaDB [yourschema]> CREATE TABLE `splitit` (
    ->   `id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
    ->   `d` VARCHAR(32) DEFAULT NULL,
    ->   age INT(11) AS (SUBSTRING_INDEX(d, ',', 1)) PERSISTENT,
    ->   weight INT(5) AS (SUBSTRING_INDEX(d, ',', -1)) PERSISTENT,
    ->   PRIMARY KEY (`id`),
    ->   INDEX idx_age (age),
    ->   INDEX idx_weight (weight)
    -> ) ENGINE=INNODB DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.79 sec)

MariaDB [yourschema]> INSERT INTO splitit (d) VALUES ('11,234'),('2,66'),('5,2');
Query OK, 3 rows affected (0.06 sec)
Records: 3  Duplicates: 0  Warnings: 0

MariaDB [yourschema]> SELECT * FROM splitit;
+----+--------+------+--------+
| id | d      | age  | weight |
+----+--------+------+--------+
|  1 | 11,234 |   11 |    234 |
|  2 | 2,66   |    2 |     66 |
|  3 | 5,2    |    5 |      2 |
+----+--------+------+--------+
3 rows in set (0.00 sec)

MariaDB [yourschema]>