How to count or know the number of rows a table has without scaning all the table, maybe using ROW_NUMBER?
If you need a exact count, you will need to do a COUNT(*) which will scan the clustered index.
You can get a rough count using the sys.partitions schema, as shown here http://www.kodyaz.com/articles/sql-rowcount-using-sql-server-system-view-sys-partitions.aspx
Update: To get the count into a variable:
DECLARE #cnt INT;
SELECT #cnt = SUM(rows)
FROM sys.partitions
WHERE
index_id IN (0, 1)
AND object_id = OBJECT_ID('MyDB.dbo.MyTable');
SELECT #cnt;
SELECT COUNT(*) FROM Table
will return the number of rows
There is no ROW_NUMBER in SQL Server, just Oracle. Use:
SELECT COUNT(primary_key) FROM table
Where primary key the primary key column of your table.
Since its a primary key, its is already indexed, so SQL can count it without scanning the whole table (it uses a clustered index to be precise, which is much faster than a full table scan)
You could also use sys.indexes schema, but its not accurate, and you would need database admin priviledges to access, and your application database user is not supposed to have grants in that schema
A little late to the party here, but in SQL Server 2005 on, you could also use the sp_spaceused stored procedure:
DECLARE #rowCount AS INT
DECLARE #spaceUsed TABLE(
[Name] varchar(64),
[Rows] INT,
[Reserved] VARCHAR(50),
[Data] VARCHAR(50),
[Index_Size] VARCHAR(50),
[Unused] VARCHAR(50)
)
INSERT INTO #spaceUsed EXEC sp_spaceused 'MyTableName'
SET #rowCount = (SELECT TOP 1 [Rows] FROM #spaceUsed)
SELECT #rowCount AS 'Row Count'
I've gotten into the habit of using sp_spaceused in place of SELECT COUNT(*) FROM Table because it is much faster. It will most likely not be as accurate as COUNT(*), however.
MSDN: http://msdn.microsoft.com/en-us/library/ms188776.aspx
I dont believe you mean this but ill give it a try:
select count(*) from table
Related
I need to Need to fetch all the records of table "#Tbl1" which "DisplayId" not present in table "#Tbl2".
"#Tbl1" having Max 100 records
"#Tbl2" is growing table
Create Table #Tbl1(Id1 Int Identity(1,1), DisplayId Nvarchar(200), Name Nvarchar(200))
Insert Into #Tbl1(DisplayId, Name) Values ('d1', 'ABC'),('d2', 'PQR')
Create Table #Tbl2(Id2 Int Identity(1,1), DisplayId Nvarchar(200))
Insert Into #Tbl2(DisplayId) Values ('d1')
Below query is working, but looking for efficient query and please suggest what kind of Index is required to which table's column?
I am using SQL Server 2008 R2
Select * From #Tbl1
Where DisplayId Not In (Select DisplayId From #Tbl2)
Using the in statement does seem to be slow generally, I would use an exists statement if possible but I'm not sure if it is supported on SQL Server 2008. Other option you have is a left join which will also be slow.
An exists or (not exists) statement works like this
select * from #tbl1 t1
where not exists (select displayid from #tbl2 where displayid = t1.displayid)
Notice the use of the alias t1, you do not have to select a column in the sub select, you can use a wildcard *. I've found this type of query is far more efficient because it uses the index links directly between the 2 tables instead of first selecting all the columns and then filtering them.
I have a function that returns a single row in SQL Server. Now I have several (about a couple hundred) databases on that server with the same table structure. I want to run that function on all the databases. Is it necessary to create the function in each database, or is there another way?
This is on SQL Server 2005, btw.
I'm not at liberty to post the actual function, but it's just an SQL Server function that returns a row. Something similar to this
ALTER FUNCTION [dbo].[getTotalOrdersByProductID](#ProductID bigint, #month varchar(100), #year varchar(100))
RETURNS #retTotalOrder TABLE
(
ProductID BIGINT primary key,
total int
)
AS
BEGIN;
INSERT #retTotalOrder
SELECT ProductID, count(*) AS total
FROM
PRODUCTS
WHERE PRODUCTS.orderdate BETWEEN firstDayOfMonth(#month, #year) AND lastDayOfMonth(#month, #year)
GROUP BY ProductID
RETURN
END;
Use . notation
SELECT * FROM Server.Database1.dbo.TableName WHERE example = 12345
SELECT * FROM Server.Database2.dbo.TableName WHERE example = 12345
You can UNION the results, depends what you wants from your function.
SELECT LAST_INSERT_ID() as id FROM table1
Why does this query sometimes return the last inserted id of another table other than table1?
I call it in Node.js (db-mysql plugin) and I can only do queries.
LAST_INSERT_ID() can only tell you the ID of the most recently auto-generated ID for that entire database connection, not for each individual table, which is also why the query should only read SELECT LAST_INSERT_ID() - without specifying a table.
As soon as you fire off another INSERT query on that connection, it gets overwritten. If you want the generated ID when you insert to some table, you must run SELECT LAST_INSERT_ID() immediately after doing that (or use some API function which does this for you).
If you want the newest ID currently in an arbitrary table, you have to do a SELECT MAX(id) on that table, where id is the name of your ID column. However, this is not necessarily the most recently generated ID, in case that row has been deleted, nor is it necessarily one generated from your connection, in case another connection manages to perform an INSERT between your own INSERT and your selection of the ID.
(For the record, your query actually returns N rows containing the most recently generated ID on that database connection, where N is the number of rows in table1.)
SELECT id FROM tableName ORDER BY id DESC LIMIT 1
I usually select the auto-incremented ID field, order by the field descending and limit results to 1. For example, in a wordpress database I can get the last ID of the wp_options table by doing:
SELECT option_id FROM wp_options ORDER BY option_id DESC LIMIT 1;
Hope that helps.
Edit - It may make sense to lock the table to avoid updates to the table which may result in an incorrect ID returned.
LOCK TABLES wp_options READ;
SELECT option_id FROM wp_options ORDER BY option_id DESC LIMIT 1;
Try this. This is working
select (auto_increment-1) as lastId
from information_schema.tables
where table_name = 'tableName'
and table_schema = 'dbName'
Most easy way:
select max(id) from table_name;
I only use auto_increment in MySQL or identity(1,1) in SQL Server if I know I'll never care about the generated id.
select last_insert_id() is the easy way out, but dangerous.
A way to handle correlative ids is to store them in a util table, something like:
create table correlatives(
last_correlative_used int not null,
table_identifier varchar(5) not null unique
);
You can also create a stored procedure to generate and return the next id of X table
drop procedure if exists next_correlative;
DELIMITER //
create procedure next_correlative(
in in_table_identifier varchar(5)
)
BEGIN
declare next_correlative int default 1;
select last_correlative_used+1 into next_correlative from correlatives where table_identifier = in_table_identifier;
update correlatives set last_correlative_used = next_correlative where table_identifier = in_table_identifier;
select next_correlative from dual;
END //
DELIMITER ;
To use it
call next_correlative('SALES');
This allows you to reserve ids before inserting a record. Sometimes you want to display the next id in a form before completing the insertion and helps to isolate it from other calls.
Here's a test script to mess around with:
create database testids;
use testids;
create table correlatives(
last_correlative_used int not null,
table_identifier varchar(5) not null unique
);
insert into correlatives values(1, 'SALES');
drop procedure if exists next_correlative;
DELIMITER //
create procedure next_correlative(
in in_table_identifier varchar(5)
)
BEGIN
declare next_correlative int default 1;
select last_correlative_used+1 into next_correlative from correlatives where table_identifier = in_table_identifier;
update correlatives set last_correlative_used = next_correlative where table_identifier = in_table_identifier;
select next_correlative from dual;
END //
DELIMITER ;
call next_correlative('SALES');
If you want to use these workarounds:
SELECT id FROM tableName ORDER BY id DESC LIMIT 1
SELECT MAX(id) FROM tableName
It's recommended to use a where clause after inserting rows. Without this you are going to have inconsistency issues.
in my table inv_id is auto increment
for my purpose this is worked
select `inv_id` from `tbl_invoice`ORDER BY `inv_id` DESC LIMIT 1;
how to write query for following request?
my table:
id designation
1 developer,tester,projectlead
1 developer
1 techlead
if id=1,designation="'developer'"
Then need to first,second records.Because 2 rows are having venkat.
if id=1,designation="'developer','techlead'" then need to get 3 records as result.
i wrote one service for inserting records to that table .so that i am maintaining one table to store all designation with same column with comas.
By using service if user pass id=1 designation="'developer','techlead'" then need to pull the above 3 records.so that i am maintaining only one table to save all designations
SP:
ALTER PROCEDURE [dbo].[usp_GetDevices]
#id INT,
#designation NVARCHAR (MAX)
AS
BEGIN
declare #idsplat varchar(MAX)
set #idsplat = #UserIds
create table #u1 (id1 varchar(MAX))
set #idsplat = 'insert #u1 select ' + replace(#idsplat, ',', ' union select ')
exec(#idsplat)
Select
id FROM dbo.DevicesList WHERE id=#id AND designation IN (select id1 from #u1)
END
You need to use the boolean operators AND and OR in conjunction with LIKE:
IF empid = 1 AND (empname LIKE '%venkat%' OR empname LIKE '%vasu%')
The above example will return all rows with empid equals 1 and empname containing venkat or vasu.
Apparently you need to create that query based on the input from user, this is just an example of how the finally query should look like.
Edit: Trying to do this within SqlServer can be quite hard so you should really change your approach on how you call the stored procedure. If you can't do this then you could try and split your designation parameter on , (the answers to this question show several ways of how to do this) and insert the values into a temporary table. Then you can JOIN on this temporary table with LIKE as described in this article.
I have a table that contains computer login and logoff events. Each row is a separate event with a timestamp, machine name, login or logoff event code and other details. I need to create a SQL procedure that goes through this table and locates corresponding login and logoff event and insert new rows into another table that contain the machine name, login time, logout time and duration time.
So, should I use a cursor to do this or is there a better way to go about this? The database is pretty huge so efficiency is certainly a concern. Any suggested pseudo code would be great as well.
[edit : pulled from comment]
Source table:
History (
mc_id
, hs_opcode
, hs_time
)
Existing data interpretation:
Login_Event = unique mc_id, hs_opcode = 1, and hs_time is the timestamp
Logout_Event = unique mc_id, hs_opcode = 2, and hs_time is the timestamp
First, your query will be simpler (and faster) if you can order the data in such a way that you don't need a complex subquery to pair up the rows. Since MySQL doesn't support CTE to do this on-the-fly, you'll need to create a temporary table:
CREATE TABLE history_ordered (
seq INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
hs_id INT,
mc_id VARCHAR(255),
mc_loggedinuser VARCHAR(255),
hs_time DATETIME,
hs_opcode INT
);
Then, pull and sort from your original table into the new table:
INSERT INTO history_ordered (
hs_id, mc_id, mc_loggedinuser,
hs_time, hs_opcode)
SELECT
hs_id, mc_id, mc_loggedinuser,
hs_time, hs_opcode
FROM history ORDER BY mc_id, hs_time;
You can now use this query to correlate the data:
SELECT li.mc_id,
li.mc_loggedinuser,
li.hs_time as login_time,
lo.hs_time as logout_time
FROM history_ordered AS li
JOIN history_ordered AS lo
ON lo.seq = li.seq + 1
AND li.hs_opcode = 1;
For future inserts, you can use a trigger like below to keep your duration table updated automatically:
DELIMITER $$
CREATE TRIGGER `match_login` AFTER INSERT ON `history`
FOR EACH ROW
BEGIN
IF NEW.hs_opcode = 2 THEN
DECLARE _user VARCHAR(255);
DECLARE _login DATETIME;
SELECT mc_loggedinuser, hs_time FROM history
WHERE hs_time = (
SELECT MAX(hs_time) FROM history
WHERE hs_opcode = 1
AND mc_id = NEW.mc_id
) INTO _user, _login;
INSERT INTO login_duration
SET machine = NEW.mc_id,
logout = NEW.hs_time,
user = _user,
login = _login;
END IF;
END$$
DELIMITER ;
CREATE TABLE dummy (fields you'll select data into, + additional fields as needed)
INSERT INTO dummy (columns from your source)
SELECT * FROM <all the tables where you need data for your target data set>
UPDATE dummy SET col1 = CASE WHEN this = this THEN that, etc
INSERT INTO targetTable
SELECT all columns FROM dummy
Without any code that you're working on.. it'll be hard to see if this approach will be any useful.. There may be some instances when you really need to loop through things.. and some instances when this approach can be used instead..
[EDIT: based on poster's comment]
Can you try executing this and see if you get the desired results?
INSERT INTO <your_target_table_here_with_the_three_columns_required>
SELECT li.mc_id, li.hs_time AS login_time, lo.hs_time AS logout_time
FROM
history AS li
INNER JOIN history AS lo
ON li.mc_id = lo.mc_id
AND li.hs_opcode = 1
AND lo.hs_opcode = 2
AND lo.hs_time = (
SELECT min(hs_time) AS hs_time
FROM history
WHERE hs_time > li.hs_time
AND mc_id = li.mc_id
)