I'm working on a application for which I need to read m rows at a time out of total 'N' rows where m < N. Every time I read 'm' rows I have to set their status as read in the same table.
For example consider following table
+------+-------------------------+--------------------------+----------+-------+---------+------+
| ID | from_email_address | to_email_address | subject | body | inqueue | sent |
+------+-------------------------+--------------------------+----------+-------+---------+------+
| 1 | 0120sushil#gmail.com | kumar.sushil#outlook.com | Subject1 | Body1 | 0 | 0 |
| 2 | 0120ksushil#gmail.com | kumar.sushil#outlook.com | Subject1 | Body1 | 0 | 0 |
| 3 | shivaseth1#gmail.com | kumar.sushil#outlook.com | Subject1 | Body1 | 0 | 0 |
| 4 | shivaseth1#gmail.com | amanrajg#outlook.com | Subject1 | Body1 | 0 | 0 |
| 5 | shivamprakash#gmail.com | amanrajg#outlook.com | Subject1 | Body1 | 0 | 0 |
| 6 | shivamprakash#gmail.com | poorvanagpal#outlook.com | Subject1 | Body1 | 0 | 0 |
| 7 | shivankgupta#gmail.com | poorvanagpal#outlook.com | Subject1 | Body1 | 0 | 0 |
+------+-------------------------+--------------------------+----------+-------+---------+------+
I want to read lets say 3 rows at a time and once I have read the rows I want to set inqueue status of those rows as 1.
I can use following query in stored procedure to select the rows
select * from EmailQueue where inqueue=1 LIMIT 3
After this how to update the same rows and set their inqueue to 1.
EDIT
Here is the stored procedure I created which is giving some error.
DELIMITER $$
DROP PROCEDURE IF EXISTS GetUnsentMails;
CREATE PROCEDURE GetUnsentMails()
BEGIN
START TRANSACTION;
CREATE TEMPORARY TABLE temp_EmailQueue AS SELECT * FROM EmailQueue WHERE inqueue = 0 LIMIT 5 FOR UPDATE;
UPDATE EmailQueue SET inqueue=1 where id in (SELECT id from temp_EmailQueue) AND inqueue = 0;
COMMIT;
END
It gives following error on calling
ERROR 1746 (HY000): Can't update table 'emailqueue' while 'temp_EmailQueue' is being created.
Suggesting to use Transaction and "SELECT FOR UPDATE" to fulfill your requirements.
Please refer following links for the examples:
MySQL 'select for update' behaviour
http://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html
http://www.sqlines.com/mysql/how-to/select-update-single-statement-race-condition
UPDATE - Added the QUERY EXAMPLE:
Example:
.......
#Before starting procedure
.......
START TRANSACTION;
CREATE TEMPORARY TABLE zzz_EmailQueue AS SELECT * FROM EmailQueue WHERE inqueue=1 LIMIT 3 FOR UPDATE;
.....
.....
#Section for other activities....
.....
.....
UPDATE EmailQueue SET inqueue=<<New_Value>> WHERE id IN (SELECT id FROM zzz_EmailQueue) AND inqueue=1;
COMMIT;
.......
#Remaining lines of Prodecure
.......
Update **
**Try with following method:
DECLARE v_EmailQueue_ID DOUBLE;
SELECT ID INTO v_EmailQueue_ID FROM EmailQueue WHERE inqueue = 0 LIMIT 1 FOR UPDATE;
UPDATE EmailQueue SET inqueue=1 WHERE id=v_EmailQueue_ID AND inqueue = 0;
Related
I am trying to use a simple code to increment only the values in the “chat_id” column of a table.
For the table lz_chat_archive_dup1, the column “chat_id” is has empty strings (no values). This is the partial excerpt of the table :
mysql> select chat_id, fullname from lz_chat_archive_dup1 LIMIT 5;
+---------+--------------+
| chat_id | fullname |
+---------+--------------+
| | Yw |
| | Shah |
| | Sunny Duhel |
| | Leong Zi Yin |
| | Mohd Nasir |
+---------+--------------+
5 rows in set (0.00 sec)
I tried to insert a value for the name “Yw” like this and it worked :
mysql> UPDATE lz_chat_archive_dup1 SET chat_id = '383933' where fullname = 'Yw';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
So now the table is like this :
mysql> select chat_id, fullname from lz_chat_archive_dup1 LIMIT 5;
+---------+--------------+
| chat_id | fullname |
+---------+--------------+
| 383933 | Yw |
| | Shah |
| | Sunny Duhel |
| | Leong Zi Yin |
| | Mohd Nasir |
+---------+--------------+
5 rows in set (0.00 sec)
However, the number of rows in this table is 2589, and for me to do it one by one is tedious and time consuming :
mysql> select count(*) from lz_chat_archive_dup1;
+----------+
| count(*) |
+----------+
| 2589 |
+----------+
1 row in set (0.00 sec)
I thought I could use a code something like this to update/increment only that one column, but I don’t think this is the correct syntax for MySQL. Can you please help to correct the code to customize it to work in my situation :
DECLARE #counter int
SET #counter = 383933
UPDATE #lz_chat_archive_dup1
SET #counter = counter = #counter + 1
So with this code, what I am trying to achieve is increment the chat_id column so that the next value is always 1 integer higher than the previous one. So the first row is 383933, the next one should be 383934, 383935, 383936,…etc etc.
The table has > 2000 rows, so this is an excerpt of it :
mysql> select time, endtime, chat_id from lz_chat_archive_dup1 LIMIT 20;
+------------+------------+---------+
| time | endtime | chat_id |
+------------+------------+---------+
| 1594948770 | 1594948928 | 383933 |
| 1594950285 | 1594950542 | |
| 1594950708 | 1594951085 | |
| 1594953554 | 1594955581 | |
| 1594955956 | 1594956551 | |
| 1595215646 | 1595218410 | |
| 1595215648 | 1595216044 | |
| 1595216110 | 1595216138 | |
| 1595220816 | 1595221144 | |
| 1595221046 | 1595221584 | |
| 1595221448 | 1595221505 | |
| 1595222302 | 1595222653 | |
| 1595236468 | 1595236848 | |
| 1595236954 | 1595237033 | |
| 1595293418 | 1595293589 | |
| 1595303280 | 1595304388 | |
| 1595303410 | 1595303822 | |
| 1595303675 | 1595303986 | |
| 1595304153 | 1595306613 | |
| 1595304878 | 1595304995 | |
+------------+------------+---------+
20 rows in set (0.00 sec)
mysql>
Here is an approach using a user variable:
set #rn = 383933;
update #lz_chat_archive_dup1
set chat_id = (select #rn := #rn + 1)
order by name;
This will assign an incrementingn number to each row, following the alphabetical order of name. If there are ties, it is undefined which name will get which number (a reason why you should have a primary key column in your table).
Assuming the names are unique, you could use a join:
update lz_chat_archive_dup1 cad join
(select cad2.*, row_number() over () as seqnum
from lz_chat_archive_dup1 cad2
) cad2
on cad2.name = cad.name
set count = seqnum + 383933;
I think this might be the recommended approach in MySQL 8+. (The statement on the deprecation of variables is a little vague on whether it would apply to UPDATE.)
You can also use variables. The problem with your statement is:
SET #counter = counter = #counter + 1
This is not even setting the column in the table! It is setting a variable. Use := to set parameters. And I strongly recommend parentheses. So, you can do:
DECLARE #counter int;
SET #counter = 383933;
UPDATE #lz_chat_archive_dup1
SET counter = (#counter := #counter + 1);
Or, in a single statement:
UPDATE #lz_chat_archive_dup1 cad CROSS JOIN
(SELECT #counter := 383933) params
SET cad.counter = (#counter := #counter + 1);
If you can live with numbers starting from 1, following the alphabetic order of your fullname column, you can try with a helper table to run the update:
CREATE TABLE updtab
AS
SELECT
ROW_NUMBER() OVER(ORDER BY fullname) AS chat_id
, fullname
FROM lz_chat_archive_dup1;
Then , run the update:
UPDATE lz_chat_archive_dup1
SET chat_id = (
SELECT chat_id
FROM updtab
WHERE updtab.fullname=lz_chat_archive_dup1.fullname
)
;
I have a problem with fetching data separated by a comma. I want the
Here is my problem
Table
ID | TDNO | PREVIOUS_TD |
1 | 14 | 13,12,11 |
2 | 23 | 45,12 |
3 | 32 | 89 |
4 | 55 | NEW |
I want to have a result like this. Example when the user will choose 14 in TD the result should be like this:
ID | TD |
1 | 14 |
2 | 13 |
3 | 12 |
4 | 11 |
And when the user will choose 32 in TD the result should be like this:
ID | TD |
1 | 32 |
2 | 89 |
when the user will select 23 the result should be like this:
ID | TD |
1 | 23 |
2 | 45 |
3 | 12 |
how to achieve this?
You might try a stored procedure or function in your version of SQL. This is MySql pseudo code and could be very buggy. Some SQL flavors do not support returning tables:
create function returnCommaSepList (IN myId INT)
begin
--
-- is mtId in the source table?
SET #previousTD = (
select PREVIOUS_TD
from TheTable
where ID = myId
)
--
-- if the result is NULL then id was not in the table, return
if #previousTD IS NULL then return
--
-- create a temporary table
create table #temp (
id INT primary key autoincrement,
td int
)
--
-- add myId to the temp table
insert into #temp (td) values(myId)
--
-- prepare to do the string handling. Step through
-- #previousTD looking for commas
SET #startPos = 0
SET #commaPos = LOCATE(',', #previousTD, #startPos)
--
-- #commaPos will be NULL if the string is NULL
if #commaPos IS NULL then return
--
-- #commaPos will be 0 if there are no commas in the string
if #commaPos = 0 then
SET #previousTD = TRIM(#previousTD)
--
-- if #previousTD is empty then return
if LENGTH(#previousTD) = 0 then return
--
-- #previousTD has something in it that is not a comma.
-- try to insert it and return
insert into #temp (td) values(#previousTD)
select * from #temp order bu id
return
endif
--
-- should have a #previousTD with at least 1 comma
while #commaPos > 0
begin
SET #item = substring(#previousTD, #startPos, #commaPos)
insert into #temp (td) values(TRIM(#item))
SET #startPos = #commaPos + 1
SET #commaPos = LOCATE(',', #previousTD, #startPos)
end
select * from #temp order bu id
end
In order to make your database, you need to create a new table which has Id of Td and tdNos and have relationships with this. for example:
Table TdNos
ID | TDNO | PREVIOUS_TD |
1 | 14 | 13,12,11 |
2 | 23 | 45,12 |
3 | 32 | 89 |
4 | 55 | NEW |
Table TdNoHistory
TdID|Priority| PREVIOUS_TD |
1 | 1 | 13 |
1 | 2 | 12 |
1 | 3 | 11 |
2 | 1 | 45 |
2 | 2 | 12 |
3 | 1 | 89 |
Which for the second table the combination of TdId and Priority are the primary key and it has a relation with table TdNos through TdId column
I am a beginner with MySQL. I made a stored procedure to insert 1,000 random names from a table. It has 3 fields with num, course_name and grade. num is foreign key--as this was for a test purpose, I just kept incremented the num only. So I didn't mark it as a PRIMARY KEY/AUTO_INCREMENT. I called the procedure, and it inserted 1,000 random names in the table. Unknowingly, I called the procedure again, and stopped it after some time. Then the table got 500 more entries after that previous 1000 entries. I wanted to delete the rows that created after the second procedure call.
Below is my statements in a stored procedure: (course_name and grade_details are additional tables with course names and grades.)
DELIMITER //
CREATE PROCEDURE course_grade(IN name_entries int)
BEGIN
DECLARE i int DEFAULT 0;
DECLARE course varchar(20);
DECLARE crs_grade char(1);
gradeloop : LOOP
SELECT name INTO course FROM course_name ORDER BY rand() LIMIT 1;
SELECT grade INTO crs_grade FROM grade_details ORDER BY rand() LIMIT 1;
INSERT INTO tbl_grade(fk_int_roll_no,vchr_course,vchr_grade)
VALUES (i+1,course,crs_grade);
SET i = i + 1;
IF (i=name_entries)
THEN LEAVE gradeloop;
END IF;
END LOOP gradeloop;
SELECT COUNT(*) FROM tbl_grade;
END //
DELIMITER ;
And my table is like :
+----------------+-------------+------------+
| fk_int_roll_no | vchr_course | vchr_grade |
+----------------+-------------+------------+
| 1 | AE | A |
| 2 | MECH | B |
| 3 | EC | A |
| . | .... | . |
| . | .... | . |
| 1000 | IT | E |
| 1 | MARINE | F |
| 2 | BIOTECH | F |
| . | .... | . |
| . | .... | . |
| . | .... | . |
| . | .... | . |
| 500 | RM | A |
+----------------+-------------+------------+
Wanted to delete the last 1 to 500 rows made by mistake!
The goal here is to update and concatenate a text field from one table to another based on conditions. When a text col gets updated with some text from a user form, run After update trigger.
The trigger runs but updates all the columns not just the one that has changed.Trying to understand how to just update the correct row only.
Here's what i have so far-
SQLFiddle
| ID | SUBID | SWNOTES |
|----|-------|---------| Table 1
| 1 | 40 | test |
| 2 | 60 | |
| ID | SUBID | CONTENT | SWFLAG |
|----|-------|---------|--------|
| 1 | 40 | hello | 0 | Table 2
| 2 | 60 | nothing | 0 |
CREATE TRIGGER `updatecontentnotes` AFTER UPDATE ON `tab1`
FOR EACH ROW
BEGIN
IF New.swnotes <> OLD.swnotes
THEN
Update `tab2`
Inner Join `tab1` ON `tab2`.`subid` = `tab1`.`subid`
Set `tab2`.`swflag` = '1',`tab2`.`content` = CONCAT(`tab2`.`content`, `tab1`.`swnotes`)
Where `tab2`.`subid` = `tab1`.`subid` AND `tab2`.`swflag` = '0';
END IF;
END//
And if I update the table with say:
Update `tab1`
set `swnotes` = "new"
where `subid` = '60'
I get :
| ID | SUBID | CONTENT | SWFLAG |
|----|-------|------------|--------|
| 1 | 40 | hellotest | 1 |
| 2 | 60 | nothingnew | 1 |
Now I know it is doing what I am telling it to do. I want to update just the row that is updated. Thanks for any help on this.
Since the contents of your trigger will run for every row on tab1, you need to be more restrictive in your WHERE clause so that it will only affect the rows that have been updated. Right now it updates every row on tab2
Try adding this to your trigger SQL:
From:
Where `tab2`.`subid` = `tab1`.`subid` AND `tab2`.`swflag` = '0';
To:
Where `tab2`.`subid` = `tab1`.`subid` AND `tab2`.`swflag` = '0' AND `tab2`.`id` = OLD.id;
This produces the results that I think you are looking for:
| ID | SUBID | CONTENT | SWFLAG |
|----|-------|------------|--------|
| 1 | 40 | hello | 0 |
| 2 | 60 | nothingnew | 1 |
The updated SQLFiddle is here:
http://sqlfiddle.com/#!2/9fa2d2/1/0
Basically I have two tables A and B. These are linked by unique ID's where the entries in B point to one entry in A. The entries in A and B also have a 'status' field denoting if the entry is active or not...
My questions is therefore; is it possible to link the status field of the entries in B and have them update, every time the 'status' field in A (pointed to by the unique ID) is updated? I could do this fairly easy with an SQL command however I'm wondering if there is a more automatic solution. Example:
table A
|------ID------|----status----|
| 1 | on |
| 2 | on |
|---------------|----------------|
table B
|-----eID------|------ID------|----status----|
| 1 | 1 | on |
| 2 | 1 | on |
| 3 | 2 | on |
|---------------|---------------|----------------|
I then run:
UPDATE `A` SET `status` = 'off' WHERE `ID` = 1;
And the result would be:
table A
|------ID------|----status----|
| 1 | off |
| 2 | on |
|---------------|---------------|
table B
|-----eID------|------ID------|----status----|
| 1 | 1 | off |
| 2 | 1 | off |
| 3 | 2 | on |
|---------------|---------------|----------------|
Is that possible?
Many Regards,
Andreas
i hope this trigger code can help u.
CREATE TRIGGER `abc` AFTER UPDATE ON `tablea` FOR EACH ROW BEGIN UPDATE tableb SET STATUS = new.status WHERE id = new.id;
END