The results of my SQL query include null values. How do I filter out null values?
The syntax may vary depending on the database you are using but you can explicitly exclude nulls in the where clause. For example, the following will exclude null values in the primary_author field:
SELECT
date,
primary_author,
ISBN
FROM
books
WHERE
primary_author IS NOT NULL;
My example works on every database I know, so it should work for you =)
SELECT *
FROM TABLE_NAME
WHERE COLUMN_NAME IS NOT NULL
Here you can find a simple explanation and some examples: https://www.w3schools.com/sql/sql_null_values.asp
But some times you want to replace null values for a default value, like 'X', in this case, we should know the database for correct syntax, here some examples:
Oracle:
SELECT nvl(column_name,'X')
FROM TABLE_NAME
Sqlite:
SELECT ifnull(column_name,'X')
FROM TABLE_NAME
SqlServer:
SELECT coalesce(column_name,'X')
FROM TABLE_NAME
Related
I was looking at this example. This makes it look like single quotes are not required in the where clause when you give a list of numbers. I am using an oracle database if that makes a difference.
https://www.sqlservertutorial.net/sql-server-basics/sql-server-in/
SELECT
product_name,
list_price
FROM
production.products
WHERE
list_price IN (89.99, 109.99, 159.99)
ORDER BY
list_price;
So why is toad complaining when I do this? It says invalid identifier as the error message.
This is the query that fails.
select * from table1 where id in (1, 2, 3, 4);
Toad does not complain when I do this.
select * from table1 where id in ('1', '2', '3', '4');
Check to make sure you are using your expected datatype. In my case I was using CHAR(12) thats why I needed quotes.
SELECT
COLUMN_NAME,
DATA_TYPE,
DATA_LENGTH,
DATA_PRECISION,
DATA_SCALE
FROM ALL_TAB_COLS
Where TABLE_NAME = 'table1';
If that doesn't work your table may be in capital letters so try this.
SELECT
COLUMN_NAME,
DATA_TYPE,
DATA_LENGTH,
DATA_PRECISION,
DATA_SCALE
FROM ALL_TAB_COLS
Where TABLE_NAME = upper('table1');
Since the question was about fetching different numbers, let's have a look on an easy way to do this.
Of course, if the column always holds numbers only and strings should not be allowed, we should just change its datatype.
And of course, if we just want to check for a few numbers like 1,2 and 3, we can use an IN clause like shown in the question.
But let's assume we can't change the datatype because also strings can occur and we need to accept a big range of numbers.
For example, we want to accept all numbers between 200 and 300. We dislike to write an IN clause with 101 values, don't we?
So we can use VALIDATE_CONVERSION to make sure we consider numeric entries only.
Then we use CAST AS INT to check the number should be between 200 and 300.
The query will be this one:
SELECT id
FROM table1
WHERE VALIDATE_CONVERSION(id AS NUMBER) = 1
AND CAST (id AS INT) BETWEEN 200 AND 300
ORDER BY id; -- sorting is of course not needed. Remove it if not intended.
We can try this out here: db<>fiddle
I am currently working with a MS SQL database on Windows 2012 Server
I need to query only 1 column from a table that I only have access to read, not make any kind of changes.
Problem is that the name of the column is "Value"
My code is this:
SELECT 'Value' FROM table
If I add
`ORDER BY 'Value'`
The issue is that the query is returning an empty list of results.
Things I've tried already
I tried replacing ' with `"' but this didn't work either.
I also tried writing SELECT * instead of SELECT VALUE
Using the table name in the SELECT or ORDER clauses again didn't help
You are claiming that this query:
SELECT 'Value'
FROM table
ORDER BY 'Value'
Is returning no rows. That's not quite correct. It is returning an error because SQL Server does not allow constant expressions as keys for ORDER BY (or GROUP BY for that matter).
Do not use single quotes. In this case:
SELECT 'Value' as val
FROM table
ORDER BY val;
Or, if value is a column in the table:
SELECT t.Value
FROM table t
ORDER BY t.Value;
Value is not a reserved word in SQL Server, but if it were, you could escape it:
SELECT t.[Value]
FROM table t
ORDER BY t.[Value];
it looks like your table has null values. and because of the order by all null values come first.
try to add filter like this
select Value FROM table
where Value is not null and Value <> ''
order by Value
I am newbie to the SQL.
I have a requirement where users might select any values from any of the 3 'multiple list' dropdown box. There might be cases where user can completely ignore any of the dropdown box out of the 3.
So i need a query which can handle that.
The equivalent select query with values looks like this.
SELECT * FROM TABLE WHERE
description1 LIKE '%SHK ABS%' OR
description2 LIKE '%SHK ABS%' OR
description3 LIKE '%SHK ABS%' OR
description4 LIKE '%SHK ABS%' and
**Year** in ('2017','2016') and
**Program** in ('CDPGM');
Problem:
I tried a lot but not able to write a query which accepts empty values in 'IN' clause.
Example: If user dint select any year and program, then empty values will be passed. Basically the query should act like it will ignore that columns in where clause.
Any idea how to achieve this ?
From what you posted I'm guessing you have a problem defining the blank value.
SELECT * FROM table
WHERE col_name IS NULL OR
col_name IN (<list_of_your_values>, '', 0,)
As per I understand there can be three type of empty values according to your case: NULL, Blank and Space(s).
The in clause to match those will look like:
SELECT * FROM table_name WHRE col_name in (null, '', <your other values>);
I have tested it in MySQL 5.6(latest version). For other versions/DBMSs you may need to use trim function:
SELECT * FROM table_name WHRE trim(col_name) in (null, '', <your other values>);
Edit:
For integer type column the empty valuea will be NULL only, OR you can also treat 0 as empty value:
SELECT * FROM table_name WHRE col_name in (null, 0, <your other values>);
how to
select name,family from student where name="X"
without its column name.
for example :
select "column1","column2" from student where "column1"="x"
or for example
select "1","2" from student where "1"="x"
"1" is column1
"2" is column2
i dont want to say columns name. i want to say just its number or other....
idont tired from select *. but it just for that i dont know the columns name but i know where they are. my columns name are change every i want to read the file but its data are same, and the data are in the same columns in each file.
Although you can not use field positions specifiers in the SELECT statement, the SQL standard includes the INFORMATION_SCHEMA where the dictionary of your tables is defined. This includes the COLUMNS view where all the fields of all tables are defined. And in this view, there is a field called ORDINAL_POSITION which you can use to assist in this problem.
If you query
SELECT ORDINAL_POSITION, COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'TABLE'
ORDER BY ORDINAL_POSITION
then you can obtain the column names for the ordinal positions you want. From there you can prepare a SQL statement.
You could use temp table as:
DECLARE #TB TABLE(Column1 NVARCHAR(50),...)
INSERT #TB
SELECT * FROM student
Then use it:
SELECT Column1 FROM #TB WHERE Column1='aa'
If it's a string you can do this :
Select Column1 + '' From Table
If it's a number you can do this :
Select Column1 + 0 From Table
If it's a datetime you can do this :
Select dateadd(d, 0, Column1) From Table
And similarly for other data types..
No, you can not use the ordinal (numeric) position in the SELECT clause. Only in Order by you can.
however you can make your own column alias...
Select Column1 as [1] From Table
You can use alias:
SELECT name AS [1], family AS [2] FROM student WHERE name="X"
It's just not possible. Unfortunately, they didn't think about table-valued functions, for which information_schema is not available, so good luck with that.
How do you write a SELECT statement that only returns rows where the value for a certain column is null?
Do you mean something like:
SELECT COLUMN1, COLUMN2 FROM MY_TABLE WHERE COLUMN1 = 'Value' OR COLUMN1 IS NULL
?
I'm not sure if this answers your question, but using the IS NULL construct, you can test whether any given scalar expression is NULL:
SELECT * FROM customers WHERE first_name IS NULL
On MS SQL Server, the ISNULL() function returns the first argument if it's not NULL, otherwise it returns the second. You can effectively use this to make sure a query always yields a value instead of NULL, e.g.:
SELECT ISNULL(column1, 'No value found') FROM mytable WHERE column2 = 23
Other DBMSes have similar functionality available.
If you want to know whether a column can be null (i.e., is defined to be nullable), without querying for actual data, you should look into information_schema.
Use Is Null
select * from tblName where clmnName is null
You want to know if the column is null
select * from foo where bar is null
If you want to check for some value not equal to something and the column also contains null values you will not get the columns with null in it
does not work:
select * from foo where bar <> 'value'
does work:
select * from foo where bar <> 'value' or bar is null
in Oracle (don't know on other DBMS) some people use this
select * from foo where NVL(bar,'n/a') <> 'value'
if I read the answer from tdammers correctly then in MS SQL Server this is like that
select * from foo where ISNULL(bar,'n/a') <> 'value'
in my opinion it is a bit of a hack and the moment 'value' becomes a variable the statement tends to become buggy if the variable contains 'n/a'.
select Column from Table where Column is null;
select * from tableName where columnName is null
For some reasons IS NULL may not work with some column data type. I was in need to get all the employees that their English full name is missing, I've used:
SELECT emp_id, Full_Name_Ar, Full_Name_En
FROM employees
WHERE Full_Name_En = '' or Full_Name_En is null