I am using MySQL 5.0'
I want display user defined column when there is no data in select statement.
Example,
i want to display 'No records found' when there is no data in select statement.
You should look at the MySQL function ISNULL() for that (and then use it in your SELECT statement).
If the value is not necessarily NULL than you can use the IF() function.
Related
I have database ready with data as per below screenshot, green column is customized column which I need to generate while querying data from SQL/Oracle.
Logic: If Actual_Completion_Date is not an empty/null, then bring
Actual_Completion_Date into Completion_Date else get
Schedule_Completion_Date in Completion_Date column.
Is there any way, where I should write If statement while defining column names in SQL query without stored procedure help.
If both date field contains NULL value then use simply COALESCE(). IF first one is NULL then second one value will show if it's not NULL. If first one is not null then will sshow first one value.
SELECT Activity_Details, Actual_Completion_Date
, Schedule_Completion_Date
, COALESCE(Actual_Completion_Date, Schedule_Completion_Date) AS Completion_Date
FROM tbl;
You can simply do this in the SELECT clause of your query. For example using the IF() function like this in mysql:
SELECT Activity_Details, Actual_Completion_Date, Schedule_Completion_Date, IF(Actual_Completion_Date IS NOT NULL, Actual_Completion_Date, Schedule_Completion_Date) AS Completion_Date
FROM tbl;
The IF function takes a condition that should return True or False as the first argument. If the condition evaluates to true, the second argument is returned and if it evaluates to false, the third.
In Oracle or Microsoft SQL server you would do something similar in the SELECT clause of your query, but using CASE WHEN ... THEN ... ELSE ... END
Oracle (and MySQL) both support generated columns. That means that you can add the logic as part of the table definition. I'm not sure if this is what you are asking for, but in Oracle, this looks like:
alter table t add column completion_date date generated always as
(coalesce(Actual_Completion_Date, Schedule_Completion_Date)) virtual;
This would be calculated when the table is queried and available to any query that uses the table.
I'm using Grafana to plot data from a MySQL datasource. Is it possible to, in a panel's query editor, use an IF ... THEN ... type statement. I would like to create a variable that I could put in the IF. I want the variable to be a condition, not necessarily to be used directly in the query.
For example:
//IN THE DATA SOURCE:
CREATE TABLE Example (Id INT, ANIMALS VARCHAR(15));
INSERT INTO Example VALUES (1,'Dog'), (2,'Fish'), (3,'Cat'), (4,'Lizard')
For a variable Test with values "Mammal',"Reptile", "Other":
//WHAT I'D LIKE IN GRAFANA QUERY EDITOR:
IF($Test = "Mammal") THEN
SELECT * FROM Example WHERE Id = 1 OR Id =3;
ELSE
SELECT * FROM Example WHERE Id = 2 OR Id =4;
END IF;
Is this kind of condition based query even possible? If so, what is the proper syntax to get it to work? Is there any way I can use Grafana variables to have a similar effect?
Use query. Query starts with SELECT keyword. Don't use any IF ELSE conditions before query, e.g.:
SELECT *
FROM Example
WHERE
Data IN ( ${variable:csv} )
This WHERE condition syntax will work with single value, multi value Grafana dashboard variables and also with All value (no custom All value, but blank=auto). Of course this condition is mainly for INT column types. STRING types may need different one (e.g. with LIKE and regexp matching).
Code all your logic (dependency on the dashboard variable) in the WHERE section. Use query inspector to see SQL which is generated and tweak it to correct SQL syntax.
Instead of an if, you can use or. It's really useful for conditionally checking variables:
select * from Example
where (Id in (1,3) or '$Test' != 'Mammal')
and (Id in (2,4) or '$Test' == 'Mammal')
I'm having a problem with a SQL query that must match the username of a user out of a column that contains all the users usernames.
So the column will contain something like:
|USER1|USER2|USER3|USER11|USER22|
The user have pipes on the left and right to prevent "USER1" be matched even in "USER11".
My query is
SELECT * FROM myTable WHERE CONCATUSERS LIKE ('%|' || 'USER1' || '|%')
Note that the USER1 in the query is a variable generated from our code so I must keep the concatenation syntax and I must use a standard syntax too (the code will run in mySQL, SQLServer etc..
So what is the correct way of concatenating strings in a LIKE clause?
MySQL uses the double pipes for concat. SQL Server you can use +.
SELECT *
FROM myTable
WHERE CONCATUSERS LIKE ('%' + '|user1|' + '%')
Use CONCAT.
(available on SQL server 2012 and beyond)
It has the benefit that it implicitly converts types to add the value to the string. And it's not just available on Sql Server and MySql.
SELECT * FROM myTable WHERE CONCATUSERS LIKE CONCAT('%|','USER1','|%');
Do note that in MySQL the result will be NULL if one of the concatenated values is NULL. But not on Sql Server.
It's just Oracle that's being stubborn by only allowing 2 values to that function.
So if the SQL needs to run unchanged on MySQL, a recent Sql Server AND Oracle then this should work:
SELECT * FROM myTable WHERE CONCATUSERS LIKE CONCAT(CONCAT('%|','USER1'),'|%');
You can go with CONCAT function.
As it is supported in both SQL and MySQL
SELECT *
FROM xpat
WHERE plname LIKE concat('%' ,'|user1|' ,'%');
Is there a way to retrieve the column names of a query that returns no data?
The result of this query would be empty.
Is there a way how to find the column names when there's no result?
Please note that I'm aware of solutions using DESCRIBE and select column_name from information_schema.columns where table_name='person';
but I need a more flexible solution that will fit these multicolumn queries.
Please also note that I am still using the original PHP MySQL extention (so no MySQLi, and no PDO).
If you wrap your query with the following SQL, it will always return the column names from your query, even if it is an empty query result:
select myQuery.*
from (select 1) as ignoreMe
left join (
select * from myTable where false -- insert your query here
) as myQuery on true
Note: When the results of the subquery are empty, a single row of null values will be returned. If there is data in the subquery it won't affect the output because it creates a cross-product with a single row...and value x 1 = value
Execute following command if the result of your previous query is empty
SHOW columns FROM your-table;
For more details check this.
I'm not sure if it will satisfy you but you can do this
SELECT *, COUNT(*) FROM table;
It will return null values (except last column which you can ignore) if the query is empty and you will be able to access all columns. It's not proper way of doing it and selecting names from INFORMATION_SCHEMA would be much better solution.
Please note that result is aggregated and you need to use GROUP BY to get more results if there are any.
You should ,
Select COLUMN_NAME From INFORMATION_SCHEMA.COLUMNS
Where TABLE_SCHEMA='yourdb'
AND TABLE_NAME='yourtablename';
Trying to get a check sum of results of a SELECT statement, tried this
SELECT sum(crc32(column_one))
FROM database.table;
Which worked, but this did not work:
SELECT CONCAT(sum(crc32(column_one)),sum(crc32(column_two)))
FROM database.table;
Open to suggestions, main idea is to get a valid checksum for the SUM of the results of rows and columns from a SELECT statement.
The problem is that CONCAT and SUM are not compatible in this format.
CONCAT is designed to run once per row in your result set on the arguments as defined by that row.
SUM is an aggregate function, designed to run on a full result set.
CRC32 is of the same class of functions as CONCAT.
So, you've got functions nested in a way that just don't play nicely together.
You could try:
SELECT CONCAT(
(SELECT sum(crc32(column_one)) FROM database.table),
(SELECT sum(crc32(column_two)) FROM database.table)
);
or
SELECT sum(crc32(column_one)), sum(crc32(column_two))
FROM database.table;
and concatenate them with your client language.
SELECT SUM(CRC32(CONCAT(column_one, column_two)))
FROM database.table;
or
SELECT SUM(CRC32(column_one) + CRC32(column_two))
FROM database.table;