I have just started with SQL and want to clear the basic keywords of SQL.
What is the difference between
"number" and "numeric" & "number & integer"?
While creating a table
Create table myTable
(
my_Id int(6) primary key
...
Above query Gives me an error suggesting to put null or not null before "primary key".
Do I always need to put either null or not null for the keyword integer?
If I replace int(6) with number(6), that statement works.
1."number" and "numeric" & "number & integer"?
An integer cannot take inputs such as 1.1 and the likes since float or decimal datatype handles this, while a number can take this both. I believe the reason why INT does not display it with a decimal its because its being rounded off try to input a 1.5 on an int column and you'll get a 2 instead
2.While creating a table
Create table myTable (
my_Id int(6) primary key, <--- Gives me an error suggesting to put
null or not null before "primary key". Do I always need to put either
null or not null for the keyword integer?
you need to either put a null or not null before a primary key unless I believe its been set into an Auto Increment
BTW my answer was based on MYSQL since that's what I used.. although I'm not sure if your using it since you didn't add any tags :)
for more info for this topic I think this could add a little more light to your inquiry
reference link
In MYSQL a primary key has to be a non-null value ie you will have to indicate by typing in NOT NULL You can re-write the code as follows:
my_id INT([optional]) PRIMARY KEY NOT NULL
When you want to make a Primary Key field it shouldn't be Null.
And
When you use int data type it don't have any (<value>), But number has.
SO
my_Id int not null primary key
Related
I am making a table right now, and I'm confused about what to use, because I used to use smallint(6) but it doesn't work in PostgreSQL.
If the column can only have integer values between 1 and 5 you can use a SMALLINT for it with a CHECK constraint.
For example:
create table review (
rating smallint not null check (rating between 1 and 5)
);
The NOT NULL constraint ensures the column always has values.
The CHECK constraint ensures values are always between 1 and 5, and that, for example, a value 6 won't be accepted.
I am trying to create a simple SQLite database that will allow me to store email addresses and timestamps. I have created the table like this:
$sql =<<<EOF
CREATE TABLE ENTRIES
(ID INT PRIMARY KEY NOT NULL,
EMAIL EMAIL NOT NULL,
TIMESTAMP DATETIME DEFAULT CURRENT_TIMESTAMP);
EOF;
And I am trying to insert an email like this:
$sql =<<<EOF
INSERT INTO ENTRIES (EMAIL)
VALUES (test#test.com);
EOF;
I am getting an error
NOT NULL constraint failed: ENTRIES.ID
I am assuming this is to do with the ID and autoincrement? I have read the docs and it advises against using autoincrement. Where am I going wrong?
The docs say:
If a table contains a column of type INTEGER PRIMARY KEY, then that column becomes an alias for the ROWID.
And because it becomes an alias for the ROWID, it's not necessary to explicitly specify a value.
You have INT PRIMARY KEY, not INTEGER PRIMARY KEY. If you change it to INTEGER PRIMARY KEY, it works the way you expect.
I am fairly new to SQL but have been working hard to learn. I am currently stuck on an issue with setting a primary key to have 8 digits no matter what.
I tried using INT(8) but that didn't work. Also AUTO_INCREMENT doesn't work in PostgreSQL but I saw there were a couple of data types that auto increment but I still have the issue of the keys not being long enough.
Basically I want to have numbers represent User IDs, starting at 10000000 and moving up. 00000001 and up would work too, it doesn't matter to me.
I saw an answer that was close to this, but it didn't apply to PostgreSQL unfortunately.
Hopefully my question makes sense, if not I'll try to clarify.
My code (which I am using from a website to try and make my own forum for a practice project) is:
CREATE Table users (
user_id INT(8) NOT NULL AUTO_INCREMENT,
user_name VARCHAR(30) NOT NULL,
user_pass VARCHAR(255) NOT NULL,
user_email VARCHAR(255) NOT NULL,
user_date DATETIME NOT NULL,
user_level INT(8) NOT NULL,
UNIQUE INDEX user_name_unique (user_name),
PRIMARY KEY (user_id)
) TYPE=INNODB;
It doesn't work in PostgreSQL (9.4 Windows x64 version). What do I do?
You are mixing two aspects:
the data type allowing certain values for your PK column
the format you chose for display
AUTO_INCREMENT is a non-standard concept of MySQL, SQL Server uses IDENTITY(1,1), etc.
Use a serial column in Postgres:
CREATE TABLE users (
user_id serial PRIMARY KEY
, ...
)
That's a pseudo-type implemented as integer data type with a column default drawing from an attached SEQUENCE. integer is easily big enough for your case (-2147483648 to +2147483647).
If you really need to enforce numbers with a maximum of 8 decimal digits, add a CHECK constraint:
CONSTRAINT id_max_8_digits CHECK (user_id BETWEEN 0 AND < 99999999)
To display the number in any fashion you desire - 0-padded to 8 digits, for your case, use to_char():
SELECT to_char(user_id, '00000000') AS user_id_8digit
FROM users;
That's very fast. Note that the output is text now, not integer.
SQL Fiddle.
A couple of other things are MySQL-specific in your code:
int(8): use int.
datetime: use timestamp.
TYPE=INNODB: just drop that.
You could make user_id a serial type column and set the seed of this sequence to 10000000.
Why?
int(8) in mysql doesn't actually only store 8 digits, it only displays 8 digits
Postgres supports check constraints. You could use something like this:
create table foo (
bar_id int primary key check ( 9999999 < bar_id and bar_id < 100000000 )
);
If this is for numbering important documents like invoices that shouldn't have gaps, then you shouldn't be using sequences / auto_increment
I want to ensure that only the values 'Expert', 'Average' or 'Adequate' are entered into the levelOfExpertise column of this table, however whenever I do try an enter one of those values, it returns an error saying the value entered is too short. Here is the create table query for this particular table. The the column I am referring to is levelOfExpertise:
CREATE TABLE MusicianInstrument
(
musicianNo varchar(5) not null
CONSTRAINT MI_PK1 REFERENCES Musician(musicianNo),
instrumentName varchar(50) not null
CONSTRAINT MI_PK2 REFERENCES Instrument(instrumentName),
levelOfExpertise varchar(50),
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise = 'Expert', 'Adequate', 'Avergage'),
PRIMARY KEY(musicianNo,instrumentName)
);
Any ideas how I can ensure only those three values (Expert, Adequate or Average) can be entered?
Thanks
Use the IN operator
CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
Try to change your CHECK constraint as following:
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
I suppose that you use sql server as RDBMS.
I have set-up a table using the following SQL script:
CREATE TABLE MY_TABLE (
ID NUMBER NOT NULL,
CODE VARCHAR2(40) NOT NULL,
CONSTRAINT MY_TABLE PRIMARY KEY (ID)
);
CREATE UNIQUE INDEX XUNIQUE_MY_TABLE_CODE ON MY_TABLE (CODE);
The problem is that I need to ensure that CODE does not have a leading zero for its value.
How do I accomplish this in SQL so that a 40-char value without a leading zero is stored?
CODE VARCHAR2 NOT NULL CHECK (VALUE not like '0%')
sorry - slight misread on the original spec
If you can guarantee that all INSERTs and UPDATEs to this table are done through a stored procedure, you could put some code there to check that the data is valid and return an error if not.
P.S. A CHECK CONSTRAINT would be better, except that MySQL doesn't support them.