Go by the word. Test Plan means we are planning for particular scope. We have to test on given environment withing given time frame defined in Test Plan. While the strategies will be common at organization level which is high level description about testing, what kind of testing and where etc.

Try this order:

INDEX(emailed,       -- for the `WHERE`
      user_id, id)   -- for the `ORDER BY

Note: In this context, IS NULL optimizes similar to = constant. So, I put that column first, thereby handing all the WHERE. After that, all the ORDER BY columns.

Hence, it would be performed entirely in the Index's BTree. (Cf "covering" or "Using index").

Fastest way if the data comes from a CSV file: LOAD DATA.

Next best: "batch" INSERTs -- Load 100 to 1000 rows at a time. (With 9 million rows, that will be thousands of batches, but that is OK.)

If the data can be pre-sorted, sort by the PRIMARY KEY and have the PK already included in the table definition.

Depending on various factors, it may be faster to drop (or not have) the secondary keys, load the data, then add the secondary keys in a single ALTER.

MySQL 5.0 was released in 2005; please consider upgrading. Still, my answer probably applies to all versions of MySQL and MariaDB and to MyISAM and InnoDB.

When query is executed, SQL server will produce a list of query plans and heuristically choose the plan with lower cost.

The chosen plan will be stored in the plan cache for subsequent use when it sees the same query.

When certain attributes of table change or when an index is rebuilt, then it will again produce a list of query plans again and heuristically choose one with lower cost, and store it in the plan cache.

However, the MSDN seems to indicate that estimated plan is stored in the plan cache, see below screenshot. Is that correct?

I work on sql server 2017 I have table name #countriesData data as below

my issue here How to convert countries column data separated pipe to rows .

meaning every rev and company and year will have only one country per row .

   create table #countriesData
 (
 company int,
 [Year] int,
 rev  int,
 countries varchar(500)
 )
 insert into #countriesData(company,[Year],rev,countries)
 values
 (12011,2010,121,'Egypt|France|America'),
 (12011,2011,121,'Egypt|Canda|America'),
 (12011,2012,121,'China|Canda|America'),
 (12099,2010,121,'SaudiArabia|France|America'),
 (12099,2011,121,'Egypt|Canda|German'),
 (12099,2012,121, 'China|Italy|America')

my expected result will be as below :

suppose i have two columns have pipe so how to modify query to handle two columns have pipe on same time

 create table #countriesData
 (
 company int,
 [Year] int,
 rev  int,
 countries varchar(500),
 countries1 varchar(500)
 )
 insert into #countriesData(company,[Year],rev,countries,countries2)
 values
 (12011,2010,121,'Egypt|France|America','India|France|America'),
 (12011,2011,121,'Egypt|Canda|America','India|Indonisya|America'),
 (12011,2012,121,'China|Canda|America','Pakistan|Indonisya|America'),
 (12099,2010,121,'SaudiArabia|France|America','Pakistan|sryia|America'),
 (12099,2011,121,'Egypt|Canda|German','Pakistan|Saudia|America'),
 (12099,2012,121, 'China|Italy|America','Holanda|Saudia|America')

mysqldump dumps users and roles as INSERT statements to populate data in the system tables in the mysql schema. So to dump these, you would use:

mysqldump mysql

The new tool https://dev.mysql.com/doc/refman/8.0/en/mysqlpump.html has an option for dumping users and roles as CREATE USER and GRANT statements instead:

mysqlpump --exclude-databases=% --users

I understand that the read committed snapshot isolation level holds the row versions in the tempdb.

I enabled this feature on a test database and I was expecting to see a new column (guid) get automatically added to the source data table (which I thought SQL will use to link to the record in tempdb). But there is no such column I can visibly see.

How does the read committed snapshot isolation level relate (link) the row in tempdb to the original row?

I have spent a lot of time investigating this error and couldn't find a solution.

I am trying to create a trigger function and a trigger and then call the procedure when the when () condition in the trigger evaluates to true. But I'm getting an error while creating the trigger:

ERROR:  column new.total does not exist
LINE 3:  FOR EACH ROW WHEN (new.total * 80 / 100 >= 80) EXECUTE PROCEDURE...
HINT:  Perhaps you meant to reference the column "new.total".

Trigger function:

CREATE OR REPLACE FUNCTION public.totalInventory_events()
 RETURNS trigger
 LANGUAGE plpgsql
AS $function$
BEGIN
     PERFORM pg_notify('notification', row_to_json(NEW)::text);
     RETURN NEW;
END;
$function$

Trigger:

CREATE TRIGGER trigger_on_totalinventory
 AFTER UPDATE OR INSERT ON users
 FOR EACH ROW 
 WHEN (new.total * 80 / 100 >= 80)
 EXECUTE PROCEDURE totalInventory_events();

Why the error, and how to fix it?

Updating the statistics would invalidate the plans in the cache, and the new plans would make use of the new statistics.

Further, even if there were a scenario that warranted clearing the cache, there are many much less invasive methods than restarting SQL Server, such as DBCC FREEPROCCACHE.

However, very rarely should you ever need to clear the entire cache.

Your filter

l_shipdate

Is not very selective, we can see from the plan that it was responsible for removing only 293,696 rows and it ended up needing to use 19,701,655. If it was to use an index to read those rows one by one it would probably have been much slower than the sequential scan of the table.

Should I drop it?

If this is the only query you are running and the only filter being used, then probably. Otherwise, there's not enough information to go on. The index would probably be useful if you wanted to see the rows for 1 particular day. The index might be better off with some additional columns in it. Impossible to say without knowing your application.

The usual way is to add all the column into the merged tables and leave unused columns null.

In practice, you should also consider how data are merged in the new DB: How to identify the same person or running session? What to do if there are conflict (e.g., same person has different age in different DB)?