I'm trying to create a simple table where I insert field and I do some checks in MySql. I've used Microsoft SQL relatively easy. Instead, MySql give evrrytime query errors without even specifying what's going on. Poor MySql software design apart, here's what I'm trying to do:
1 table with 4 fields with an autoincremental autogenerated number to det an ID as primary key
CREATE TABLE `my_db`.`Patients_table` (
`ID_Patient` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`Patient_name` VARCHAR( 200 ) NOT NULL ,
`Recovery_Date` DATETIME NOT NULL ,
`Recovery_count` INT NOT NULL
) ENGINE = MYISAM
a simple stored procedure to insert such fields and check if something exist before inserting:
CREATE PROCEDURE nameInsert(IN nome, IN data)
INSERT INTO Patients_table (Patient_name,Recovery_Date) values (nome,data)
IF (EXISTS (SELECT Recovery_count FROM Tabella_nomi) = 0) THEN
INSERT INTO (Patients_table (Recovery_count)
ELSE
SET Recovery_count = select Recovery_count+1 from Patients_table
END
this seems wrong on many levels and MySQL useless syntax checker does not help.
How can I do this? Thanks.
There seems to be a lot wrong with this block of code. (No offense intended!)
First, Procedures need to be wrapped with BEGIN and END:
CREATE PROCEDURE nameInsert(IN nome, IN data)
BEGIN
...[actually do stuff here]
END
Second, since your table is declared with all fields as NOT NULL, you must insert all fields with an INSERT statement (this includes the Recovery_Date column, and excludes the AUTO_INCREMENT column). You can add DEFAULT CURRENT_TIMESTAMP to the date column if you want it to be set automatically.
INSERT INTO Patients_table (Patient_name,Recovery_Date) values (nome,data)
Third, what exactly is your IF predicate doing?
EXISTS (SELECT Recovery_count FROM Tabella_nomi) = 0
If you want to check if a row exists, don't put the = 0 at the end. Also, Tabella_nomi isn't declared anywhere in that procedure. Also, your SELECT statement should have a WHERE clause, since I'm assuming you want to select a specific row (this is going to select a result set of all recovery_counts).
Fourth, the second INSERT statement seems a little messy. It should look more like the first INSERT, and keep the point I made above in mind.
INSERT INTO (Patients_table (Recovery_count)
Fifth, the ELSE statement
SET Recovery_count = select Recovery_count+1 from Patients_table
Has some problems too. SET is meant for setting variables, not values in rows. I'm not 100% sure what your intent is from this statement, but it looks like you meant to increment the Recovery_count column of a certain row if it already exists. In which case, you meant to do something like this:
UPDATE Patients_table SET Recovery_count = Recovery_count+1 WHERE <conditional predicate>
Where the conditional predicate is something like this:
Patients_name = nome
Try these things, and look at the errors it gives you when you try to execute the CREATE STATEMENT. I bet they're more useful then you think!
Related
I have a table with 3 fields: Id(PK,AI), Name(varchar(36)), LName(varchar(36)).
I have to insert name and last name, Id inserts automatically because of it's constraints,
Is There a way to Jump id auto increment value when it reaches 6?
for instance do this 7 times:
Insert Into table(Name, LName) Values ('name1', 'lname1') "And jump id to 7 if it is going to be 6"
It may sound stupid to do this but I have the doubt.
Also Jump and do not record id 6.
record only, 1-5, 7,8,9 and so on
What I want to achieve starts from a Union:
Select * From TableNames
Union All
Select * From TableNames_general
In the TableNames_general I assign it's first value so that when the user sees the table for the first time it will be displayed the record I inserted.
The problem comes when the user inserts a new record, if the Id of the inserted record is the same as the one I have inserted it will be duplicated, that is why I want to achieve when the users inserts one record and if the last insert id already exists just jump that record. this is because I must have different ids due to its relationship among child tables.
Identity column generate values for you, And its best left this way, You have the ability to insert specific values in Identity column but its best left alone and let it generate values for you.
Imagine you have inserted a value explicitly in an identity column and then later on Identity column generates the same value for you, you will end up with duplicates.
If you want to have your input in that column then why bother with identity column anyway ??
Well this is not the best practice but you can jump to a specific number by doing as follows:
MS SQL SERVER 2005 and Later
-- Create test table
CREATE TABLE ID_TEST(ID INT IDENTITY(1,1), VALUE INT)
GO
-- Insert values
INSERT INTO ID_TEST (VALUE) VALUES
(1),(2),(3)
GO
-- Set idnentity insert on to insert values explicitly in identity column
SET IDENTITY_INSERT ID_TEST ON;
INSERT INTO ID_TEST (ID, VALUE) VALUES
(6, 6),(8,8),(9,9)
GO
-- Set identity insert off
SET IDENTITY_INSERT ID_TEST OFF;
GO
-- 1st reseed the value of identity column to any smallest value in your table
-- below I reseeded it to 0
DBCC CHECKIDENT ('ID_TEST', RESEED, 0);
-- execute the same commad without any seed value it will reset it to the
-- next highest idnetity value
DBCC CHECKIDENT ('ID_TEST', RESEED);
GO
-- final insert
INSERT INTO ID_TEST (VALUE) VALUES
(10)
GO
-- now select data from table and see the gap
SELECT * FROM ID_TEST
If you query the database to get the last inserted ID, then you can check if you need to increment it, by using a parameter in the query to set the correct ID.
If you use MSSQL, you can do the following:
Before you insert check for the current ID, if it's 5, then do the following:
Set IDENTITY_INSERT to ON
Insert your data with ID = 7
Set IDENTITY_INSERT to OFF
Also you might get away with the following scenario:
check for current ID
if it's 5, run DBCC CHECKIDENT (Table, reseed, 6), it will reseed the table and in this case your next identity will be 7
If you're checking for current identity just after INSERT, you can use SELECT ##IDENTITY or SELECT SCOPE_IDENTITY() for better results (as rcdmk pointed out in comments)
Otherwise you can just use select: SELECT MAX(Id) FROM Table
There's no direct way to influence the AUTO_INCREMENT to "skip" a particular value, or values on a particular condition.
I think you'd have to handle this in an AFTER INSERT trigger. An AFTER INSERT trigger can't update the values of the row that was just inserted, and I don't think it can make any modifications to the table affected by the statement that fired the trigger.
A BEFORE INSERT trigger won't work either, because the value assigned to an AUTO_INCREMENT column is not available in a BEFORE INSERT trigger.
I don't believe there's a way to get SQL Server IDENTITY to "skip" a particular value either.
UPDATE
If you need "unique" id values between two tables, there's a rather ugly workaround with MySQL: roll your own auto_increment behavior using triggers and a separate table. Rather than defining your tables with AUTO_INCREMENT attribute, use a BEFORE INSERT trigger to obtain a value.
If an id value is supplied, and it's larger than the current maximum value from the auto_increment column in the dummy auto_increment_seq table, we'd need to either update that row, or insert a new one.
As a rough outline:
CREATE TABLE auto_increment_seq
(id INT NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE=MyISAM;
DELIMITER $$
CREATE TRIGGER TableNames_bi
BEFORE INSERT ON TableNames
FOR EACH ROW
BEGIN
DECLARE li_new_id INT UNSIGNED;
IF ( NEW.id = 0 OR NEW.id IS NULL ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NULL);
SELECT LAST_INSERT_ID() INTO li_new_id;
SET NEW.id = li_new_id;
ELSE
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END IF;
END$$
CREATE TRIGGER TableNames_ai
AFTER INSERT ON TableNames
FOR EACH ROW BEGIN
DECLARE li_max_seq INT UNSIGNED;
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END;
DELIMITER ;
The id column in the table could be defined something like this:
TableNames
( id INT UNSIGNED NOT NULL DEFAULT 0 PRIMARY KEY
COMMENT 'populated from auto_increment_seq.id'
, ...
You could create an identical trigger for the other table as well, so the two tables are effectively sharing the same auto_increment sequence. (With less efficiency and concurrency than an Oracle SEQUENCE object would provide.)
IMPORTANT NOTES
This doesn't really insure that the id values between the tables are actually kept unique. That would really require a query of the other table to see if the id value exists or not; and if running with InnoDB engine, in the context of some transaction isolation levels, we might be querying a stale (as in, consistent from the point in time at the start of the transaction) version of the other table.
And absent some additional (concurrency killing) locking, the approach outline above is subject to a small window of opportunity for a "race" condition with concurrent inserts... the SELECT MAX() from the dummy seq table, followed by the INSERT, allows a small window for another transaction to also run a SELECT MAX(), and return the same value. The best we can hope for (I think) is for an error to be thrown due to a duplicate key exception.
This approach requires the dummy "seq" table to use the MyISAM engine, so we can get an Oracle-like AUTONOMOUS TRANSACTION behavior; if inserts to the real tables are performed in the context of a REPEATABLE READ or SERIALIZABLE transaction isolation level, reads of the MAX(id) from the seq table would be consistent from the snapshot at the beginning of the transaction, we wouldn't get the newly inserted (or updated) values.
We'd also really need to consider the edge case of an UPDATE of row changing the id value; to handle that case, we'd need BEFORE/AFTER UPDATE triggers as well.
OK, this is what I want to do :
If an entry already exists (e.g. based on field name), then just return its id
If it doesn't, add it
This is what I've managed so far (for the "if doesn't exist, create it" part) :
INSERT INTO `objects` (`id`,`name`)
SELECT NULL,'someObj2' FROM `objects`
WHERE NOT EXISTS
(SELECT name FROM `objects` WHERE `name`='someObj2');
SELECT LAST_INSERT_ID();
How can I get the id (instead of LAST_INSERT_ID()) if the entry does exist?
P.S. Yep, I know that the main reason I can't get my head around SQL is the degree at which I'm used to the more classical if-then-else approach of regular programming languages... lol
UPDATE :
I keep trying and trying and this what I've managed so far (as a stored procedure) :
IF EXISTS (SELECT * FROM `objects` WHERE `name` = NAME)
THEN
SELECT `id` FROM `objects` WHERE `name` = NAME;
ELSE
INSERT INTO `objects` (`id`,`name`) VALUES(NULL,NAME);
SELECT LAST_INSERT_ID() AS 'id';
END IF
and calling it like: CALL insertObject("someObj2");
However, it's not working as expected - neither does it add the entry, nor does it return the id (instead it returns all ids in the table...). Any idea what could be going wrong?
It looks like you are trying to enforce a unique constraint on name. If so, you can also do this by just declaring the column to be unique or equivalently creating a unique index:
create unique index objects_name on objects(name);
If this is true, then change the question from getting the last inserted id to just getting the id for name:
select id
from objects o
where o.name = 'someObj2';
I hasten to add that in a high-transaction environment where things are being added and deleted quickly, any approach might have a problem. Consider your code, the row could be inserted and then deleted, even before the last_insert_id() is executed. If you are dealing with a high transaction environment with potential race conditions, then you need to use transactions and locking to do what you want.
I am using mysql database.
I have a field user_type in USER table. I would like to restrict the values in this field to be one of ('ADMIN','AGENT','CUSTOMER').
The insert statements should fail if they tried to insert anything else than the above possible values. Also, I need defaulting to 'CUSTOMER' is none is specified in the insert statements.
The possible solution I could think of is use of triggers, but I would like to know How this could be handled more efficiently (possibly in the create table ddl itself?).
Any ideas, How to do this?
This is what the column type "enum" is for. You treat it like a string, and behind the scenes it is stored as an int, and must be one of the values defined in the DDL:
CREATE TABLE users (
id int unsigned NOT NULL auto_increment primary key,
user_type enum('ADMIN', 'AGENT', 'CUSTOMER') NOT NULL default 'CUSTOMER'
)
Then insert like so:
INSERT INTO users (user_type) VALUES ('ADMIN'); // success
INSERT INTO users (user_type) VALUES ('ANONYMOUS'); // failure (or '' if not "strict" mode)
INSERT INTO users (user_type) VALUES (default(user_type)); // uses default
INSERT INTO users () VALUES (); // uses default
INSERT INTO users (user_type) VALUES (NULL); // failure
note
Note that for the query to actually fail, you must use "SQL strict mode". Otherwise, an "empty string" value (which is slightly special in that it has the numeric value of 0) is inserted.
Quoting this docs page:
When this manual refers to “strict mode,” it means a mode where at least one of STRICT_TRANS_TABLES or STRICT_ALL_TABLES is enabled.
I came across this post, and as it dates somewhat back, I was thinking of others coming across it these days too and miss the (in my opinion) simpler approach of simply adding a CHECKconstraint (e.g. this for MySQL, or this for MariaDB).
In my opinion, using a CHECK constraint is much easier than using things like ENUM and / or SET as you don't need to worry about the relations to integer indexes etc. when relying on them. They for example can become weird when you try to preset allowed integer values for a column.
Example, where you want to have a column which has values ranging from 1 to 5:
CREATE TABLE myTable (
myCol INT NOT NULL
CONSTRAINT CHECK (0 < `myCol` < 5)
);
To be more clear:
The table thetable (id int, username varchar(30), password varchar(30), last_successful_login timestamp, last_unsuccessful_login timestamp, another_variable varchar(30)) has the following row: (1, "tgh", "pass", 0, 0, "another")
1) Wrong User/Pass Pair, but there is a row with the username
I want select id from thetable where username="tgh" and password="wrongpass" and another_variable="another"; to update the last_unsuccessful_login columns of all the rows with username="tgh" AND another_variable="another" (which is unique, there can't be two rows with ("tgh", "another") pair. There can be ("tgh", "another2") though.) to CURRENT_TIMESTAMP.
So the example row would be (1, "tgh", "pass", 0, CURRENT_TIMESTAMP, "another"), after the "select" query that does not completely match.
To be even more clear, I am trying to avoid running an extra update with only username="tgh" and another_variable="another" on the table, i.e. update thetable set last_unsuccessful_login=CURRENT_TIMESTAMP where username="tgh" and another_variable="another";, according to the result of the select.
2) Correct User/Pass Pair
Also, if all three username and password and another_variable matches, this time I want to set the last_successful_login to CURRENT_TIMESTAMP.
That would make the example row `(1, "tgh", "pass", CURRENT_TIMESTAMP, 0, "another")
What is the most efficient way to do this?
The short answer to your question is no, it is not possible for a SELECT statement to cause or trigger an update. (The caveat here is that a SELECT statement can call a FUNCTION (MySQL stored program) which can perform an UPDATE.)
You can't get around issuing an UPDATE statement; an UPDATE statement has to be issued from somewhere, and a SELECT statement cannot "trigger" it.
It is possible to have a single UPDATE statement do the check of the supplied password against the current value in the password column, and set both the last_successful_login and last_unsuccessful_login columns, e.g.:
UPDATE thetable
SET last_successful_login =
IF(IFNULL(password,'')='wrongpass',CURRENT_TIMESTAMP,0)
, last_unsuccessful_login =
IF(IFNULL(password,'')='wrongpass',0,CURRENT_TIMESTAMP)
WHERE username='tgh'
AND another_variable='another'
So, you could issue an UPDATE statement first; and then issue a SELECT statement.
If you want to minimize the number of "roundtrips" to the database, at the cost of additional complexity (making it harder for someone else to figure out what is going on) you could put the UPDATE statement into a stored program. If you put this into a function, you could set the return value to indicate whether the login was successful.
SELECT udf_login('username','wrongpass','another')
So, from your application, it looks like you are doing a login check, but the called function can perform the UPDATE.
CREATE FUNCTION `udf_login`
( as_username VARCHAR(30)
, as_password VARCHAR(30)
, as_another_variable VARCHAR(30)
) RETURNS INT
READS SQL DATA
BEGIN
UPDATE `thetable`
SET `last_successful_login` =
IF(IFNULL(`password`,'')=IFNULL(as_password,''),CURRENT_TIMESTAMP,0)
, `last_unsuccessful_login` =
IF(IFNULL(`password`,'')=IFNULL(as_password,''),0,CURRENT_TIMESTAMP)
WHERE `username` = as_username
AND `another_variable` = as_another_variable;
-- then perform whatever checks you need to (e.g)
-- SELECT IFNULL(t.password,'')=IFNULL(as_password,'') AS password_match
-- FROM `thetable` t
-- WHERE t.username = as_username
-- AND t.another_variable = as_another_variable
-- and conditionally return a 0 or 1
RETURN 0;
END$$
Using strictly SQL (no PHP or anything else), is it possible to create a table and insert default data into that table only if that table doesn't exist?
Use the CREATE TABLE ... SELECT format:
create table if not exists tablename as
select * from defaultdata;
Here is one way of doing it:
CREATE TABLE IF NOT EXISTS T (
ID int(10) unsigned NOT NULL primary key,
NAME varchar(255) NOT NULL
);
REPLACE INTO T SELECT 1, 'John Doe';
REPLACE INTO T SELECT 2, 'Jane Doe';
REPLACE is a MySQL extension to the SQL standard that either inserts, or deletes and inserts.
You might do a select on the one of the meta data tables
if(not exists select * from whatever_meta where table_name = "whatever)
begin
...
end
You would have to do some research to figure out how exactly...
Can you store the table status as a variable, then use that variable to determine whether to insert data? Ex:
#status = SHOW TABLES LIKE 'my_table';
INSERT INTO my_table VALUES (1,'hello'),(2,'world') WHERE #status <> false;
The problem with Paul Morgan's answer is that it expects data to already exist in another table. Jonas' answer would be extremely resource exhaustive, especially if there's a lot of REPLACES (which are unnecessary if the table exists).
May be I am missing the point but why can't the default data be a set of insert statements...and what one simply needs to do is create the table if it does not exist followed by insert statements...that ways the default data does not have to exist in a different table.