Deleting duplicate rows from a table
I have a table in my database which has duplicate records that I want to delete. I don't want to create a new table with distinct entries for this. What I want is to delete duplicate entries from the existing table without the creation of any new table. Is there any way to do this?
id action
L1_name L1_data
L2_name L2_data
L3_name L3_data
L4_name L4_data
L5_name L5_data
L6_name L6_data
L7_name L7_data
L8_name L8_data
L9_name L9_data
L10_name L10_data
L11_name L11_data
L12_name L12_data
L13_name L13_data
L14_name L14_data
L15_name L15_data
see these all are my fields :
id is unique for every row.
L11_data is unique for respective action field.
L11_data is having company names while action is having name of the industries.
So in my data I'm having duplicate name of the companies in L11_data for their respective industries.
What I want is to have is unique name and other data of the companies in the particular industry stored in action. I hope I have stated my problem in a way that you people can understand it.
Solution 1:
Yes, assuming you have a unique ID field, you can delete all records that are the same except for the ID, but don't have "the minimum ID" for their group of values.
Example query:
DELETE FROM Table
WHERE ID NOT IN
(
SELECT MIN(ID)
FROM Table
GROUP BY Field1, Field2, Field3, ...
)
Notes:
- I freely chose "Table" and "ID" as representative names
- The list of fields ("Field1, Field2, ...") should include all fields except for the ID
- This may be a slow query depending on the number of fields and rows, however I expect it would be okay compared to alternatives
EDIT: In case you don't have a unique index, my recommendation is to simply add an auto-incremental unique index. Mainly because it's good design, but also because it will allow you to run the query above.
Solution 2:
ALTER IGNORE TABLE 'table' ADD UNIQUE INDEX(your cols);
Duplicates get NULL, then you can delete them