I have my table schema in H2 db as follows:
create table if not exists Test ( id bigint not null,name varchar(255), primary key (id) );
alter table Test add constraint if not exists Test_NAME UNIQUE (name);
I want to insert a value for the name attribute as 'Default' if it does not exist in the table by selecting the latest id value from the table and increment it by one.
Example:
Do not insert if an entry for name = Default already exists.
ID | Name
1 | Default
Insert if an entry for name = Default does not exists.
ID | Name
1 | ABC
2 | XYZ
For the id column, find the max id and increment it by one. In this case, insert id=3 and name=Default.
My query is as follows:
INSERT INTO Test (id , name)
SELECT max(id) + 1, 'Default' from Test
WHERE NOT EXISTS (SELECT * FROM Test where name='Default');
However, it gives me an error saying:
NULL not allowed for column "ID"; SQL statement
as it applies the where condition on the inner select statement.
I also tried:
MERGE INTO Test KEY(name) VALUES (SELECT MAX(id) + 1 from Test, 'Default');
It gives an error because, merge tries to update with the new values.
If it finds 'Default', it will update the row with new id causing primary key violation.
Is there a better way to do this? How can I make the query work?
You are massively overcomplicating this. Define the id field as auto increment and place a unique index on the name field. The unique index prevents duplicate names to be inserted, while the auto increment increases the value of the id field by 1 (by default) if the insert is successful.
I updated id to auto increment and the following query work flawlessly
INSERT INTO Test (name) select * from (select 'Default') as tmp WHERE NOT EXISTS (SELECT name from Test where name='Default');
when you run your query first time, no record found in table so, it give error 'null' there, so if you add IFNULL() function there as below
INSERT INTO Test (id , name)
SELECT **IFNULL**(max(id),0) + 1, 'Default'
FROM Test
WHERE NOT EXISTS (SELECT * FROM Test where name='Default');
Related
I would like to insert a row in the middle of my SQL table. Similar to Excel, the existing rows should then be automatically increased by ID+1. Is there such a function?
Example:
Current state:
After insert inbetween:
Please never do it in production.
Setup
create table tbl(
id int NOT NULL AUTO_INCREMENT primary key,
val varchar(20)
);
insert into tbl (val)
values
('a'),('b'),('c'),('d');
The script to add 'x' between 'b' and 'c' when ordered by id
update tbl
set id=id+1
where id > 2
order by id desc;
insert tbl(id, val)
values (3,'x');
I've got the following table:
productId price
1 price_value1
2 price_value2
3 price_value3
I would like to insert a new product into the table and assign it a new productId. In this case its value equals to 4.
So I want my new table to look like so:
productId price
1 price_value1
2 price_value2
3 price_value3
4 price_value4
So as far as I understand, in order to do that I have to somehow retrieve the max value of productId and insert it using INSERT INTO mytable VALUES (productId + 1, price_value4).
But how do I find out the maximum value of productId?
I tried INSERT INTO mytable VALUES (SELECT MAX(productId) + 1 FROM mytable, price_value4) but it didn't work.
This should Work:
Select the max(productID) and price_value4 as a columns from mytable and insert the result.
INSERT INTO mytable (SELECT MAX(productId) + 1, 'price_value4' FROM mytable);
However, if you are not going to jump some number you can just add an auto increment id key to product_id and then you will have only to insert the price, the product ID will be incremented automatically..
This will do so :
ALTER TABLE mytable
MODIFY COLUMN `productId` INT(10) UNSIGNED PRIMARY KEY AUTO_INCREMENT;
you can change INT(10) with the INT(5) for example depanding on the size you want to give to your productId column
EDIT :
In return to the OP question in comments why his solution wouldn't work
Some suggetions says you have to make the SELECT statment in insert always between parenthesis
INSERT INTO mytable VALUES ( (SELECT MAX(ID)+1 FROM mytable) , price_value4)
.. In my Case it Return
(1093): You can't specify target table
'mytable' for update in FROM clause
AND HERE IS WHY (Quoting From the documentation)
When selecting from and inserting into the same table, MySQL creates
an internal temporary table to hold the rows from the SELECT and then
inserts those rows into the target table. However, you cannot use
INSERT INTO t ... SELECT ... FROM t when t is a TEMPORARY table,
because TEMPORARY tables cannot be referred to twice in the same
statement
BUT there is away to overcome by using a query instead of the table itself in the FROM, which has the effect of copying the requested table values instead of referencing the one that you are updating..
INSERT INTO mytable VALUES (
(SELECT MAX(ID)+1 FROM (SELECT * FROM mytable ) as mytmp ),
'price_value4');
OR (Quoting From the documentation)
To avoid ambiguous column reference problems when the SELECT and the
INSERT refer to the same table, provide a unique alias for each table
used in the SELECT part, and qualify column names in that part with
the appropriate alias.
INSERT INTO mytable Values ( (SELECT MAX(ID)+1 FROM mytable as mytmp) , 'price_value4')
This is a duplicate question. In order to take advantage of the auto-incrementing capability of the column, do not supply a value for that column when inserting rows.
A simple syntax to create table
CREATE TABLE Product (
productId MEDIUMINT NOT NULL AUTO_INCREMENT,
price INT NOT NULL,
PRIMARY KEY (productid)
);
While inserting supplied default or leave column as blank or supplied value as NULL. Take a look at below code snippet.
INSERT INTO Product (price) VALUES
('10'),('20'),('4'),
('30');
refer this link
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 have CSV files and I need to do something like this before inserting data in my table:
table fields
id = primary id and auto-increment
house_no
city_code
prv_code
cty_code
if (house_no,city_code,prv_code,cty_code) exists = ignore insert
else if (house_no,city_code,prv_code,cty_code) is null = ignore insert
else (house_no,city_code,prv_code,cty_code) !exist = insert
My original code just re-inserts the same values because the primary key id is just creating a new id for it and as a result I have duplicates.
I need to do this to avoid duplicates. I tried INSERT IGNORE and REPLACE but I need a unique key and all fields may have a value which is the same (like they may have different house_no but the same prv_code or cty_code or something like that). I just want to check if the record exist before I insert it.
You can create a unique key over more than one column. In your case you need an unique key containing of the four columns house_no, city_code, prv_code and cty_code.
In your case:
ALTER TABLE fields
ADD CONSTRAINT uc_fieldsUnique UNIQUE (house_no,city_code,prv_code, cty_code);
Load data from CSV-file into second table, and then use INSERT like this to add rows -
INSERT INTO t1(id, house_no, city_code, prv_code, cty_code)
SELECT NULL, t2.house_no, t2.city_code, t2.prv_code, t2.cty_code FROM t2
LEFT JOIN t1 ON t1.house_no = t2.house_no AND t1.city_code = t2.city_code AND t1.prv_code = t2.prv_code AND t1.cty_code = t2.cty_code
WHERE t1.id IS NULL
(rename table names)
I have a simple table like this
CREATE TABLE authid(
id INT NOT NULL AUTO_INCREMENT,
authid VARCHAR(128) NOT NULL UNIQUE,
PRIMARY KEY(id)
);
Now if I insert a value with
INSERT INTO authid(authid) VALUES('test');
It will work fine and return the inserted id the first time, but if I do it again when the authid already exists (notice that we have authid marked as UNIQUE) it will return an error.
Is there a way achieve this this in one SQL statement: Insert it, get the id and if it already exists, still get the id.
Take a look at this: http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
If you're using MySQL 5.0 or higher you can use the "INSERT ... ON DUPLICATE KEY UPDATE" syntax. You may be able to combine that with LAST_INSERT_ID() (I'm not positive about that)
So:
insert into authid (authid) values ('test') on duplicate key update id=LAST_INSERT_ID(id), authid='test';
select LAST_INSERT_ID();
Well indeed if you try to insert 2 times the same value in a UNIQUE field, it won't work, that's the point of UNIQUE fields.
If I understand well, you want to know if it's possible whether to use an INSERT or an UPDATE statement depending on the existance of an item or not ? Then you need 2 queries, 1 to test existence, the other to insert new value or update existing one
Insert the value conditionally (i.e. if it doesn't exist). Whether the insert takes place or not, by the end of the statement the result will be the same: the value will be in the table. So, just select the ID of the row that matches that value. Or, speaking in SQL, like this:
INSERT INTO authid (authid)
SELECT 'test'
WHERE NOT EXISTS (
SELECT *
FROM authid
WHERE authid = 'test'
);
SELECT id
FROM authid
WHERE authid = 'test'
;