The following SQL statement will create a table t, with a column c1, whose type is defined as bigint(21) unsigned, which is the returning type of function INET_ATON:
CREATE TABLE t AS SELECT INET_ATON('0.0.0.0') AS c1;
But the statement also inserts a row. I wonder if there is a way to create the table and make its columns' type defined as some function's returning type, without inserting a row.
I tried the following:
CREATE TABLE t LIKE SELECT INET_ATON('0.0.0.0') AS c1;
But this doesn't match the SQL syntax.
Any ideas on how to achieve this? Thanks!
PS: Any standard SQL statement is OK, the MariaDB or MySQL supported statement is also OK.
use where clause to create a condition which will never be true like below:
CREATE TABLE t AS SELECT INET_ATON('0.0.0.0') AS c1 where 1=2;
This will create the table without adding any rows into it.
Related
I have a table called matchresults which has five columns named mresultid, playerid, seasonmatchid, rank, ratingsearned
mresultid is the primary key and playerid and seasonmatchid are foreign keys
The problem is that when I try to create a view on this table:
DROP VIEW IF EXISTS matchresults_view;
CREATE VIEW matchresults_view AS
select mresultid, playerid, seasonmatchid
from matchresults
where id = 8 ;
The query runs but it says mysql returned an empty result set. This is not true as I should be having two tuples in the result set.
What is wrong with the query?
Well, you are creating a view. This command does not return any rows. It simply creates a view which you can think of as SQL query saved under a name, so that it is later possible to use in your queries. It will still execute the underlying SQL statement.
Now you have to query the view like below, to see what it outputs:
select * from matchresults_view
I'm trying to write a query to select the results of a stored procedure into a temp table. However the stored procedure has been set up so that when it runs its returns 1 result with no alias. (See below)
obviously I get an error when I try and select the data into a temp table.
An object or column name is missing or empty. For SELECT INTO
statements, verify each column has a name. For other statements, look
for empty alias names. Aliases defined as "" or [] are not allowed.
Change the alias to a valid name.
Is there any way round this as I will be unable to update the procedure to output an alias! Basically Im after a way of doing a
SELECT * INTO #tmptable
FROM OPENROWSET ('SQLNCLI', 'Server=ServerName;Trusted_Connection=yes;','SET FMTONLY OFF EXEC sp_name')
If you know how many columns you will get back from the OPENROWSET, then you can create the temporary table before inserting values; this allows you to give the columns a name.
CREATE TABLE #tmptable (Value INT NOT NULL)
INSERT #tmptable
SELECT * FROM OPENROWSET ('SQLNCLI','Server=ServerName;Trusted_Connection=yes;','SET FMTONLY OFF EXEC sp_name')
-- DROP TABLE #tmptable
If you do not know how many columns you are returning... I do not know that it is possible.
I'm trying to create a cleaned-up table that replaces a varchar(50) field with an integer. The original field has occasional text values that I'd like to convert to 0 or null values.
I can do this in a select statement just fine, but get an error when trying to create my table.
Below is a minimal example that uses strings:
/* This works */
DROP TABLE IF EXISTS mytest;
CREATE TABLE mytest
AS
SELECT convert("123", unsigned) AS mynum;
/* This works, returning a row of 0 */
SELECT convert("TEST", unsigned) AS mynum;
/* But this fails, with: Truncated incorrect INTEGER value: 'TEST'*/
DROP TABLE IF EXISTS mytest;
CREATE TABLE mytest
AS
SELECT convert("TEST", unsigned) AS mynum;`
What is wrong with the above, and is there a better way to accomplish what I want? Thanks for the help.
I don't have an explanation for why that error occurs, but I found a workaround using a subquery:
DROP TABLE IF EXISTS mytest;
CREATE TABLE mytest
AS
SELECT mynum
FROM (SELECT convert("TEST"), unsigned) AS mynum) t;
Demo: http://www.sqlfiddle.com/#!2/4909a/1
I'd use a case statement for it and also switch over to using CAST instead of convert so you'll get failures instead of implicit conversions.
CREATE TABLE mytest(myVarchar varchar(10));
INSERT mytest VALUES ('123'),('TEST');
SELECT CASE
WHEN myVarchar REGEXP '^[0-9]+$' THEN CAST(myVarchar,unsigned)
ELSE 0
END As mynum
FROM mytest;
I don't have a mysql instance handy to test this so hopefully I didn't goof any syntax errors.
Rather than convert, you could update the data and then alter the table:
UPDATE mytest SET mynum=mynum + 0;
ALTER TABLE mytest CHANGE COLUMN mynum mynum INT UNSIGNED;
It looks like you are implicitly defining the column name by the select statement in the create. This may be assuming the "TEST" string is the datatype. It would help to see the error message you get, but my assumption would be to explicitly define the column as:
CREATE TABLE mytest(mynum int);
Then
Insert into mytest(mynum)
select convert("TEST",unsigned) as mynum;
This is also why the answer with the subquery may work, by the time it gets to the outer query it is implicitly defined as an int.
I would like to get count of specific records. So my query will look like the following...
SELECT
ID,
NAME,
(SELECT...) AS UserCount // Stmt1
FROM MyTable
The issue is that, 'Stmt1' is a complex statement and it cannot be written as innerquery.
Well, I can use functions, but the statement includes 'CREATE TABLE' so I get the following error message
Cannot access temporary tables from within a function.
What is the best way to accomplish the task ?
You can use user defined table type to solve your problem.
You just create a table variable like
CREATE TYPE [dbo].[yourTypeName] AS TABLE(
[columeName1] [int] NULL,
[columeName2] [varchar](500) NULL,
[columeName3] [varchar](1000) NULL
)
GO
and you can declare this table variable in your function like
CREATE FUNCTION [dbo].[yourFunctionName]
(
#fnVariable1 INT ,
#yourTypeNameVariable yourTypeName READONLY
)
RETURNS VARCHAR(8000)
AS
BEGIN
SELECT .................
FROM #yourTypeNameVariable
WHERE ........
RETURN #r
END
On your procedure you can declare your table type like
DECLARE #yourTypeNamevaribale AS yourTypeName
And you can insert values to this table like
insert into #yourTypeNamevaribale (col,col,..)values(val,val,..)
pass this to your function like
dbo.yourFunctionName(fnVariable1 ,#yourTypeNamevaribale )
please go for this method, thank you
Yes you can not use #temp table.
As you are using SQL Server 2008, why don't you use table variable instead of #temp tables?
Give it a try.
I came across this post as I started using table variables and switched to temporary tables for performance reasons only to find temporary tables couldn't be used in a function.
I would be hesitant about using table variables especially if you are playing with large result sets, as these are held in memory. See this post...
http://totogamboa.com/2010/12/03/speed-matters-subquery-vs-table-variable-vs-temporary-table/
Other alternatives would be..
Extracting the temporary table result into another table function.
Converting the code into using sub-queries
In 99,99% of cases there is no need for any tricks with temp tables or subqueries, but use aggregation functions like COUNT, SUM or AVG in combination with OVER clause and (often) PARTITION BY.
I am not sure what the OP tried to achieve but I assume that the UserCount is somehow related to the values in MyTable. So there must be a way to join MyTable to whatever table that produces UserCount.
The most simple example is to show all users and the total number of users
SELECT id
, name
, user_count = COUNT(*) OVER()
FROM MyUsers
I've recently moved from MSSQL to MySQL.
I would like to use a table variable (or equivalent) inside a MySQL 5.5 stored routine, to populate a dataset for an online report.
In MS SQL, I would do it this way
...
...
DECLARE #tblName TABLE
WHILE <condition>
BEGIN
Insert Row based on iteration value
END
...
...
From what I understand, I can't declare table variables in MySQL (correct me if I'm wrong) How do I implement the above logic in a MySQL stored procedure?
You could create a table or temporary table and populate it with data you need.
CREATE TABLE Syntax
You understand that limitation correctly. The MySQL user manual clearly states that user-defined variables cannot refer to a table:
http://dev.mysql.com/doc/refman/5.5/en/user-variables.html
User variables are intended to provide data values. They cannot be used directly in an SQL statement as an identifier or as part of an identifier, such as in contexts where a table or database name is expected, or as a reserved word such as SELECT.
create temporary table tmp
(
id int unsigned not null,
name varchar(32) not null
)
engine=memory; -- change engine type if required e.g myisam/innodb
insert into tmp (id, name) select id, name from foo... ;
-- do more work...
select * from tmp order by id;
drop temporary table if exists tmp;
I think this covers it. Also, this may be helpful.