I am trying to concatenate two integers as the default value in a third field. My create table in SQL Server works fine:
CREATE TABLE MEI_Tbl
(
MEI_ID int PRIMARY KEY IDENTITY (1,1),
SRC tinyint NOT NULL DEFAULT '2',
HEI_ID AS (Cast (SRC as varchar)+ Cast (MEI_ID as varchar))
);
but when I try to create it in MySQL, I cannot find the equivalent for the concatenation of the two integers (Line 5 HEI_ID...).
**
I am aware of changing IDENTITY (1,1) to AUTO_INCREMENT for MySQL.
**
I have also tried several concat methods, but to no avail.
MySQL seems happier if I define the datatype for HEI_ID, and I have done so as varchar and int but again no success.
I have spent too much time reading about tool kits to convert SQL Server to MySQL. I just want to create the table in MySQL.
Any input would be appreciated.
MySQL does not support computed columns. Instead, you can use a view:
CREATE TABLE MEI_Tbl (
MEI_ID int PRIMARY KEY AUTO_INCREMENT,
SRC tinyint NOT NULL DEFAULT 2
);
CREATE VIEW v_MEI_Tbl as
SELECT MEI_ID, SRC,
CONCAT(src, mei_d) as HEI_ID
FROM MEI_Tbl
);
Then query from the view.
Related
I'm new to this website and using Mysql and phpMyAdmin. I need help with one of my table and I would really appreciate it. So, I created a table that has an Integer column I want to be able to limit it to only 7(Seven) digits I'm not quiet sure if this is possible using Mysql or phpMyAdmin.
I haven't tried any query on it. I want to limit the Integer type to only 7(Seven) digits.
This might not be the best possible solution but I think that if you were to store the integer as string in the format char(7) to limit the number of characters able to be entered it would get the job done.
I'm not familiar with Mysql in particular but here's some documentation on it : https://dev.mysql.com/doc/refman/8.0/en/char.html
I hope this helped.
In MySQL <8.0.16 You can't restrict the number of digits for an Integer. That has no meaning.
You can, however, use a DECIMAL type that allows you to specify the number of digits and the number of decimal places.
For example, DECIMAL(7,0) will define what you want.
Your CREATE statement becomes something like
CREATE TABLE IF NOT EXISTS myTable (
id INT AUTO_INCREMENT PRIMARY KEY,
someText VARCHAR(255) NOT NULL,
decimalValue DECIMAL(7,0)
) ;
If you're using MySQL 8.0.16 or later you can use a CHECK constraint to limit the value (as distinct from limiting the number of digits).
The example above becomes
CREATE TABLE IF NOT EXISTS myTable (
id INT AUTO_INCREMENT PRIMARY KEY,
someText VARCHAR(255) NOT NULL,
decimalValue INT,
CONSTRAINT `decValue_chk` CHECK (`decimalValue` <= 9999999))
) ;
I am using SSMA for MySQL tool to migrate data from MySQL to SQL Server 2016. After migration data completed. The field value of float type from MySQL table is different from SQL Server field. In MySQL table, the value is 90177104, but in SQL Server table, the value is 90177100.
Can anyone please explain why the values are different? Is it a bug of SSMA? If so, is there any workaround to make the two values the same? Thanks!
MySQL table schema:
create table test
(
id int auto_increment
primary key,
value float null
);
# insert data.
insert into test(value) values(90177104);
SQL Server table schema:
create table test
(
id int identity
constraint table_name_pk
primary key nonclustered,
value float default NULL
)
More a display than storage thing.
drop table if exists t,TEST;
create table t
(
id int auto_increment
primary key,
value float(20,1) null,
val2 float null
);
# insert data.
insert into t(value,VAL2) values(90177104,90177104);
SELECT T.* ,CAST(`VALUE` AS DECIMAL),CAST(`VAL2` AS DECIMAL) FROM T;
# id, value, val2, CAST(`VALUE` AS DECIMAL), CAST(`VAL2` AS DECIMAL)
'1', '90177104.0', '90177100', '90177104', '90177104'
Im revisiting my database and noticed I had some primary keys that were of type INT.
This wasn't unique enough so I thought I would have a guid.
I come from a microsoft sql background and in the ssms you can
choose type to "uniqeidentifier" and auto increment it.
In mysql however Ive found that you have to make triggers that execute on insert for the tables you want
to generate a guide id for. Example:
Table:
CREATE TABLE `tbl_test` (
`GUID` char(40) NOT NULL,
`Name` varchar(50) NOT NULL,
PRIMARY KEY (`GUID`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
Trigger:
CREATE TRIGGER `t_GUID` BEFORE INSERT ON `tbl_test`
FOR EACH ROW begin
SET new.GUID = uuid();
Alternatively you have to insert the guid yourself in the backend.
Im no DB expert but still remember that triggers cause performance problems.
The above is something I found here and is 9 years old so I was hoping something has changed?
As far as stated in the documentation, you can use uid() as a column default starting version 8.0.13, so something like this should work:
create table tbl_test (
guid binary(16) default (uuid_to_bin(uuid())) not null primary key,
name varchar(50) not null
);
This is pretty much copied from the documentation. I don't have a recent enough version of MySQL at hand to test this.
You can make a
INSERT INTO `tbl_test` VALUES (uuid(),'testname');
This would generate a new uuid, when you call it.
Or you can also use the modern uuid v4 by using one of these functions instead of the standard uuid(), which is more random than the uuid in mysql
How to generate a UUIDv4 in MySQL?
You can use since 8.0.13
CREATE TABLE t1 (
uuid_field VARCHAR(40) DEFAULT (uuid())
);
But you wanted more than unique, but here are only allowed internal functions and not user defined as for uuid v4, for that uyou need the trogger
As per the documentation, BINARY(x) adds some hidden padding bytes to the end of each entry, & VARCHAR(40) also wastes space by not being encoded directly in binary. Using VARBINARY(16) would be more efficient.
Also, more entropy (unguessability / security) per byte is available from RANDOM_BYTES(16) than standardized UUIDs, because they use some sections to encode constant metadata.
Perhaps the below will work for your needs.
-- example
CREATE TABLE `tbl_test` (
`GUID` VARBINARY(16) DEFAULT (RANDOM_BYTES(16)) NOT NULL PRIMARY KEY,
`Name` VARCHAR(50) NOT NULL
);
Im revisiting my database and noticed I had some primary keys that were of type INT.
This wasn't unique enough so I thought I would have a guid.
I come from a microsoft sql background and in the ssms you can
choose type to "uniqeidentifier" and auto increment it.
In mysql however Ive found that you have to make triggers that execute on insert for the tables you want
to generate a guide id for. Example:
Table:
CREATE TABLE `tbl_test` (
`GUID` char(40) NOT NULL,
`Name` varchar(50) NOT NULL,
PRIMARY KEY (`GUID`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
Trigger:
CREATE TRIGGER `t_GUID` BEFORE INSERT ON `tbl_test`
FOR EACH ROW begin
SET new.GUID = uuid();
Alternatively you have to insert the guid yourself in the backend.
Im no DB expert but still remember that triggers cause performance problems.
The above is something I found here and is 9 years old so I was hoping something has changed?
As far as stated in the documentation, you can use uid() as a column default starting version 8.0.13, so something like this should work:
create table tbl_test (
guid binary(16) default (uuid_to_bin(uuid())) not null primary key,
name varchar(50) not null
);
This is pretty much copied from the documentation. I don't have a recent enough version of MySQL at hand to test this.
You can make a
INSERT INTO `tbl_test` VALUES (uuid(),'testname');
This would generate a new uuid, when you call it.
Or you can also use the modern uuid v4 by using one of these functions instead of the standard uuid(), which is more random than the uuid in mysql
How to generate a UUIDv4 in MySQL?
You can use since 8.0.13
CREATE TABLE t1 (
uuid_field VARCHAR(40) DEFAULT (uuid())
);
But you wanted more than unique, but here are only allowed internal functions and not user defined as for uuid v4, for that uyou need the trogger
As per the documentation, BINARY(x) adds some hidden padding bytes to the end of each entry, & VARCHAR(40) also wastes space by not being encoded directly in binary. Using VARBINARY(16) would be more efficient.
Also, more entropy (unguessability / security) per byte is available from RANDOM_BYTES(16) than standardized UUIDs, because they use some sections to encode constant metadata.
Perhaps the below will work for your needs.
-- example
CREATE TABLE `tbl_test` (
`GUID` VARBINARY(16) DEFAULT (RANDOM_BYTES(16)) NOT NULL PRIMARY KEY,
`Name` VARCHAR(50) NOT NULL
);
How can we add a constraint which enforces a column to have only positive values.
Tried the following mysql statement but it doesn't work
create table test ( test_column integer CONSTRAINT blah > 0);
You would use the keyword unsigned to signify that the integer doesn't allow a "sign" (i.e. - it can only be positive):
CREATE TABLE test (
test_column int(11) unsigned
);
You can read more about the numeric data types (signed & unsigned) here.
As far as an actual constraint to prevent the insertion-of negative values, MySQL has a CHECK clause that can be used in the CREATE TABLE statement, however, according to the documentation:
The CHECK clause is parsed but ignored by all storage engines.
For reference, here is how you would use it (and though it will execute absolutely fine, it just does nothing - as the manual states):
CREATE TABLE test (
test_column int(11) unsigned CHECK (test_column > 0)
);
UPDATE (rejecting negative values completely)
I've noticed from a few of your comments that you want queries with negative values to be completely rejected and not set to 0 (as a normal transaction into an unsigned column would do). There is no constraint that can do this in-general (that I know of, at least), however, if you turn strict-mode on (with STRICT_TRANS_TABLES) any query that inserts a negative value into an unsigned column will fail with an error (along with any-other data-insertion errors, such as an invalid enum value).
You can test it by running the following command prior to your insert-commands:
SET ##SESSION.sql_mode = 'STRICT_TRANS_TABLES';
And if it works for you, you can either update your MySQL config with sql-mode="STRICT_TRANS_TABLES" or use SET ##GLOBAL.sql_mode = 'STRICT_TRANS_TABLES'; (I'm not sure if the SET command will affect the global mysql config though, so it may be better to update the actual config-file).
As of MySQL 8.0.16 (MariaDB 10.2.1), CHECK constraints are enforced. (In earlier versions constraint expressions were accepted in the syntax but ignored).
Therefore you can use:
CREATE TABLE test (
test_column INT CHECK (test_column > 0)
);
or
CREATE TABLE test (
test_column INT,
CONSTRAINT test_column_positive CHECK (test_column > 0)
);
The way to fix this is to explicitly tell MySQL Server to create an Unsigned integer.
CREATE TABLE tbl_example (
example_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
example_num INT UNSIGNED NOT NULL,
example_text TEXT
PRIMARY KEY (`example_id`)
);
just use unsigned to allow only positive values.
CREATE TABLE hello
(
world int unsigned
);
SQLFiddle demo
uncomment the line and you will see the error saying: Data truncation: Out of range value for column 'world' at row 1:
You should use UNSIGNED INTEGER data type. For more information, click here