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Can a foreign key be NULL and/or duplicate?
...mply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by definition is not a value. Null means that we do not yet know what the value is.
Let me give you a real life example. Suppose you have a database that sto...
How to check if a table exists in a given schema
Postgres 8.4 and greater databases contain common tables in public schema and company specific tables in company schema.
company schema names always start with 'company' and end with the company number.
So there may be schemas like:
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Count table rows
What is the MySQL command to retrieve the count of records in a table?
11 Answers
11
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Html table tr inside td
I am trying to create a table in HTML. I have the following design to create. I had added a <tr> inside the <td> but somehow the table is not created as per the design.
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How to get all columns' names for all the tables in MySQL?
Is there a fast way of getting all column names from all tables in MySQL , without having to list all the tables?
10 Answe...
Truncating all tables in a Postgres database
...pgSQL can do this. Here's the script:
CREATE OR REPLACE FUNCTION truncate_tables(username IN VARCHAR) RETURNS void AS $$
DECLARE
statements CURSOR FOR
SELECT tablename FROM pg_tables
WHERE tableowner = username AND schemaname = 'public';
BEGIN
FOR stmt IN statements LOOP
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LAST_INSERT_ID() MySQL
...hat I think must be quite easy. I need to return the LAST INSERTED ID from table1 when I run the following MySql query:
11 ...
Difference between local and global indexes in DynamoDB
...l Secondary Indexes still rely on the original Hash Key.
When you supply a table with hash+range, think about the LSI as hash+range1, hash+range2.. hash+range6.
You get 5 more range attributes to query on.
Also, there is only one provisioned throughput.
Global Secondary Indexes defines a new paradi...
Delete all data in SQL Server database
How I can delete all records from all tables of my database? Can I do it with one SQL command or I need for one SQL command per one table?
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How to see indexes for a database or table in MySQL?
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To see the index for a specific table use SHOW INDEX:
SHOW INDEX FROM yourtable;
To see indexes for all tables within a specific schema you can use the STATISTICS table from INFORMATION_SCHEMA:
SELECT DISTINCT
TABLE_NAME,
INDEX_NAME
FROM INFORM...