How to concatenate text from multiple rows into... - Stack Overflow
To avoid null values you can use CONCAT(). DECLARE @names VARCHAR(500) SELECT @names = CONCAT(@names, ' ', name) FROM Names select @names.
Функция CONCAT - сложение строк при выборке | Трепачёв Дмитрий
Функция CONCAT предназначена для сложения строк при выборке из базы данных. Строками обычно выступают поля таблиц.
4 Ways to Replace NULL with a Different Value in MySQL
Sometimes you want NULL values to be returned with a different value, such as “N/A”, “Not Applicable”, “None”, or even the empty string “”.
Как за 30 минут бесплатно проверить свой... — Разработка на vc.ru
FROM (SELECT(SLEEP(5)))geJr) Type: UNION query Title: Generic UNION query (NULL) - 4 columns Payload: id=2 UNION ALL SELECT NULL,CONCAT(0x716a6a6b71...
COUNT (Transact-SQL) - SQL Server | Microsoft Docs
При этом учитываются и строки, содержащие значения NULL.
SQL NULL Values - IS NULL and IS NOT NULL
The IS NULL operator is used to test for empty values (NULL values). The following SQL lists all customers with a NULL value in the "Address" field: Example. SELECT CustomerName, ContactName, Address FROM Customers WHERE Address IS NULL
A PostgreSQL story about "NULL IS NULL = NULL AND NOT NULL"
First of all: NULL is a super useful thing in SQL and people should be aware of the details associated with it. Before digging deeper into NULL it is necessary to take a look at the most basic rules. The following example shows a mistake commonly made by many developers
Заметка про NULL / Хабр
select 1 from dual where dummy = null; -- запрос не вернёт записей.
Working with SQL NULL values
How to Count SQL NULL values in a column? The COUNT() function is used to obtain the total number of the rows in the result set.
MySQL 1064 Error: You have an error in your SQL syntax
SELECT * from students WHERE studentID =. Since there is nothing there, the MySQL engine gets confused and complains via a 1064 error.