I have a MYSql table with columns id,name,description and status. The id column is auto incremented and is primary key. Now, I want to add another column to the table named 'display_priority'. I want the records to be pulled using 'order by' on this column.
How can I auto populate this table(based on ID), while inserting records?
The display_priority values do not matter while inserting. It shall be rearranged later on, at some point of time, before displaying the records. But, the inserted values need to be unique.
Any help? Thanks in advance.
Edit: I know that this can be done by an after insert trigger. What if, I wanted to avoid a trigger. Any other way?
You take max id of the table and add 1 as auto-incremented id prediction.
INSERT INTO `table_name` (col1, col2, col3)
SELECT val1, val2, max(id) + 1 AS val3 FROM `table_name`;
<!-- id is auto-incremented -->
Example
INSERT INTO `users` (name, email, display_priority)
SELECT 'Dave', 'dave#email.com', max(id) + 1 AS display_priority FROM `users`;
If you want to avoid TRIGGER you could use the current UNIX_TIMESTAMP or CURRENT_TIMESTAMP as a default value. But if tow or more INSERT at the same second you have a problem ...
display_priority TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
You could add a TRIGGER witch update the display_priority on insert and the value is the maximum of display_priority plus one.
CREATE TRIGGER table_name BEFORE INSERT ON display_priority
FOR EACH ROW SET #sum = (SELECT MAX(display_priority)+1 FROM table_name);
Related
ALTER TABLE advance_d ADD testcolumn INTEGER NOT NULL AUTO_INCREMENT;
This is the sql code i typed. i have a table called advace_d. It has a primary key column called "ad_id" . when i wrote this code ALTER TABLE advance_d ADD testcolumn INTEGER; a new column was created with null values. I want to know how to create the column with values starting from a given value auto incremented by 1.
so my table would have 1 primary key column for ID and another column with values starting from 50 incremented by 1.
The only way I know how to do this is via insertion into a table with an auto increment column. I don't know how to do this with your existing table, but you can create a new one, and then copy the previous table over to it, populating the auto increment column in the process:
CREATE TABLE newTable (col1, col2, ..., colAuto INT NOT NULL AUTO_INCREMENT);
INSERT INTO newTable (col1, col2, ..., colAuto)
SELECT col1, col2, ..., NULL -- NULL for colAuto
FROM yourTable
ORDER BY ad_id;
This should result in a new table with the same data, and a column colAuto which starts as 1, as ordered by the ad_id column in your original table. After this, you may alter colAuto if you don't want it to be auto increment anymore. You may also delete the original table if it no longer serves any purpose.
Edit:
We might also be able to do this using a row number session variable:
SET #rn := 0;
UPDATE yourTable
SET colAuto = (SELECT #rn := #rn + 1 )
ORDER BY ad_id;
But in practice, doing such an update into a non auto increment column may not make much business sense. This is because as soon as you add more data to your table, you would have to manually update again, but this time the sequence would be starting from some number other than zero. Really, an auto increment column is the way to go for easily maintaining a sequence in SQL.
I need two columns in table that would have same value on insert. Is there any way to do it from database side?
So you want to let one column use the auto_increment feature, but make another column in the same table also have the same value?
I can't think of a reason you would need this feature. Perhaps you could explain what you're trying to accomplish, and I can suggest a different solution?
A trigger won't work for this. It's a chicken-and-egg problem:
You can't change any column's value in an AFTER trigger.
But the auto-increment value isn't set yet when a BEFORE trigger executes.
It also won't work to use a MySQL 5.7 GENERATED column:
CREATE TABLE MyTable (
id INT AUTO_INCREMENT PRIMARY KEY,
why_would_you_want_this INT GENERATED ALWAYS AS (id)
);
ERROR 3109 (HY000): Generated column 'why_would_you_want_this'
cannot refer to auto-increment column.
You can't do it in a single SQL statement. You have to INSERT the row, and then immediately do an UPDATE to set your second column to the same value.
CREATE TABLE MyTable (
id INT AUTO_INCREMENT PRIMARY KEY,
why_would_you_want_this INT
);
INSERT INTO MyTable () VALUES ();
UPDATE MyTable SET why_would_you_want_this = LAST_INSERT_ID()
WHERE id = LAST_INSERT_ID();
You could alternatively generate the ID value using some other mechanism besides AUTO_INCREMENT (for example a Memcached incrementing key). Then you could insert the new value in both columns:
INSERT INTO MyTable (id, why_would_you_want_this) VALUES ($gen_id, $gen_id);
Define a before or after insert trigger and assign the value of the 2nd field in the trigger.
If the 1st field is an auto increment column, then you need to use an after insert trigger. If your application assigns value to the 1st field, then you can use a before insert trigger.
However, I would no necessarily duplicate the value on insert. You can leave the 2nd field as null on insert, which would mean that its value is the same as the 1st field's. The only drawback of this approach is that it may be more difficult to create joins on the 2nd field.
You can do this in one query by using the primary key (assumed to be id) and setting your column (assumed to be columnName):
"INSERT INTO tableName SET `columnName` = (SELECT MAX(x.id) FROM tableName x)+1"
This will not work if you have deleted the most recent primary key row however. To get past this, you can insert into the id as well:
"INSERT INTO tableName SET `columnName` = (SELECT MAX(x.id) FROM tableName x)+1, `id`= (SELECT MAX(x.id) FROM tableName x)+1"
However, this solution has the downside (or upside depending on the case) of reusing primary key values that have already been deleted.
suggested way:
To use the actual auto_increment value, you can do this:
"INSERT INTO tableName SET `columnName` = (SELECT `AUTO_INCREMENT` FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'db_name' AND TABLE_NAME = 'table_name')"
Sources that helped me solve this: Prashant Pimpale's answer
I'm trying to update values already stored in a table, and I've implemented an auto-incrementing primary key column so that I can reference specific rows by number (as recommended here).
Using...
ALTER TABLE taxipassengers ADD COLUMN rid INT NOT NULL AUTO_INCREMENT PRIMARY KEY
The problem I'm running into though is that now I'm getting Column count doesn't match value count at row 1 when I insert the same data as before. It's like it wants me to give it a value for the PK. If I delete the column with the PK, the error goes away, and I'm back to square one.
Am I missing something?
EDIT: Here's the insert statement
INSERT INTO taxipassengers SELECT a.post_date, b.vendor_name, c.lastName, d.firstName, null as taxiGroup
FROM (select ID,post_date from wp_posts where post_type = 'shop_order') a,
(SELECT order_id,vendor_name FROM wp_wcpv_commissions) b,
(SELECT post_id,meta_value as lastName FROM wp_postmeta where meta_key ='_billing_last_name') c,
(SELECT post_id,meta_value as firstName FROM wp_postmeta WHERE meta_key ='_billing_first_name') d
WHERE a.ID = b.order_id and b.order_id=c.post_id and c.post_id = d.post_id;
Mind you, the insert statement worked before implementing the PK column, and it still works if I remove the PK column.
Possibly you are using this syntax to insert rows
INSERT INTO mytable VALUES (1, 'abc', 'def');
INSERT syntax from MySQL manual
The columns for which the statement provides values can be specified as follows:
If you do not specify a list of column names for INSERT ... VALUES or INSERT ... SELECT, values for every column in the table must be provided by the VALUES list or the SELECT statement. If you do not know the order of the columns in the table, use DESCRIBE tbl_name to find out.
You must add new column to your INSERT query. For autoincrement column NULL can be inserted to generate new value. And your column will be added last by default (if you don't use AFTER in ALTER TABLE).
To add a column at a specific position within a table row, use FIRST or AFTER col_name. The default is to add the column last. You can also use FIRST and AFTER in CHANGE or MODIFY operations to reorder columns within a table.
So, now your INSERT must look like this:
INSERT INTO mytable VALUES (1, 'abc', 'def', NULL); -- use NULL for autoincrement
INSERT INTO mytable (col1, col2, col3) VALUES (1, 'abc', 'def'); -- or add column names
First check if your database allows mutable PK, or prefers stable PK .
Please read through below articles, I am sure you will get what's going wrong.
http://rogersaccessblog.blogspot.in/2008/12/what-is-primary-key.html
First, the value in the primary key cannot be duplicated
Can we update primary key values of a table?
Structure table:
id (int primary key)
name (varchar 100)
date(datetime)
For insert I use query:
INSERT INTO table (name, date) VALUES ('t1','$date');
For delete row I use query:
DELETE FROM table WHERE name = 't1';
I would like want how make 1 query: first insert, if row with it name already exist, than delete row, and insert again.
Tell me please how to make it?
Create a UNIQUE index over your name column:
ALTER TABLE `table` ADD UNIQUE (name);
If you genuinely want to "delete row and insert again", then you can use REPLACE instead of INSERT. As documented:
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted.
Therefore, in your case:
REPLACE INTO `table` (name, date) VALUES ('t1','$date');
However, if instead of deleting the existing record and then inserting a new one you merely want to update the existing record, you can use INSERT ... ON DUPLICATE KEY UPDATE:
INSERT INTO `table` (name, date) VALUES ('t1','$date')
ON DUPLICATE KEY UPDATE date = VALUES(date);
The most material difference is in the treatment of columns for which you do not provide explicit values (such as id in your example): REPLACE will result in the new record having the default value, whereas INSERT ... ON DUPLICATE KEY UPDATE will result in the old value being retained.
What you want to do is use MySQL's on duplicate update feature.
Can be used like this :
INSERT INTO table (name, date) VALUES ('t1','$date')
ON DUPLICATE KEY UPDATE name=VALUES(name),dateVALUES(date);
Of course for that to happen a dupliate violation must occur.
insert into table (name, date) values('t1','$date') on duplicate key update name=values(name), date=values(date)
Are you looking for an update query?
Update will set a value on an already existing row.
UPDATE table SET date = '$newdate' WHERE name = 't1';
The best way to do this is using the mysql methods together with your query.
If you make the 'name' field unique:
id (int primary key)
name (varchar 100) NOT NULL UNIQUE
date(datetime)
And alter the query to:
INSERT INTO table
(name, date) VALUES ('t1','$date')
ON DUPLICATE KEY UPDATE date = "$date"
I am trying to populate a products table on MySQL with latest products, which are retrieved and stored in products_temp table.
So the method for this is straight forward, simply doing an INSERT to products from products_temp, as such:
INSERT INTO products ( select products_temp.* FROM products_temp )
Problem is, it results in a duplicate primary key error, because of the id from products_temp clashing with the id in products.
Can someone tell me how to fix this please?
I tried declaring the fields in the select statement without the id, but that results in "Column count doesn't match value count at row 1"
Any help would be appreciated.
Thanks!
You'll need to declare the columns except the ID on both the INSERT and the SELECT, since the number of fields need to match, and id (as you noticed) can't be inserted as is into the destination table.
INSERT INTO DestTable (field1, field2, field3)
SELECT field1, field2, field3 FROM SourceTable;
An SQLfiddle to test with.
EDIT: You could do it in a bit more hacky way to simplify the insert. You can create a trigger that simply forces the primary key to NULL on insert.
CREATE TRIGGER t_DT BEFORE INSERT ON DestTable
FOR EACH ROW
SET NEW.id = NULL;
then a copy from table to table can be done as simply;
INSERT INTO DestTable SELECT * FROM SourceTable;
Another SQLfiddle.
How about something like:
INSERT INTO products
(
select products_temp.* FROM products_temp
where key not in (select key from products)
)