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CREATE UNIQUE INDEX statement can also be used to apply the UNIQUE constraint to the field of an existing MySQL table. The syntax of it is as follows −CREATE UNIQUE INDEX index_name ON table_name(Column_name);ExampleSuppose we have the following table named ‘Test5’ and we want to add UNIQUE constraint to the column ‘ID’ then it can be done with the help of CREATE UNIQUE INDEX command as follows −mysql> DESCRIBE TEST5; +-------+-------------+------+-----+---------+-------+ | Field | Type        | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | ID    | int(11)     | YES  |   ... Read More

We can apply the UNIQUE constraint to a column of an existing MySQL table with the help of ALTER TABLE statement.SyntaxALTER TABLE table_name MODIFY colum_name datatype UNIQUE;                     OR ALTER TABLE table_name ADD UNIQUE (colum_name);ExampleSuppose we have the following table named ‘Test4’ and we want to add UNIQUE constraint to the column ‘Name’ then it can be done with the help of ALTER TABLE command as follows −mysql> DESCRIBE test4; +-------+-------------+------+-----+---------+-------+ | Field | Type        | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | ID   ... Read More

It is quite possible to insert the NULL keyword as a value in a character type column having NOT NULL constraint because NULL is a value in itself. Following example will exhibit it −ExampleSuppose we have a table test2 having character type column ‘Name’ along with NOT NULL constraint on it. It can be checked from the DESCRIBE statement as follows −mysql> Describe test2\G *************************** 1. row ***************************   Field: id    Type: int(11)    Null: NO     Key: Default: NULL   Extra: *************************** 2. row ***************************   Field: NAME    Type: varchar(20)    Null: NO     Key: ... Read More

We can remove a NOT NULL constraint from a column of an existing table by using the ALTER TABLE statement.ExampleSuppose we have a table ‘test123’ having a NOT NULL constraint on column ‘ID’ as follows −mysql> DESCRIBE test123; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra    | +-------+---------+------+-----+---------+-------+ | ID    | int(11) | NO   |     |   NULL  |       | | Date  | date    | YES  |     |   NULL  |       | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.04 sec)Now if we ... Read More

In this case, MySQL will return an error message regarding data truncated for the column. Following is an example of demonstrating it −ExampleSuppose we have a table ‘test2’ which contains a NULL value in column ‘ID’ at 2nd row. Now, if we will try to declare the column ID to NOT NULL then MySQL will return the error as follows −mysql> Select * from test2; +------+--------+ | ID   | Name   | +------+--------+ | 1    | Gaurav | | NULL | Rahul  | +------+--------+ 2 rows in set (0.00 sec) mysql> ALTER TABLE TEST2 MODIFY ID INT NOT NULL; ERROR 1265 (01000): Data truncated for column 'ID' at row 2

We can apply the NOT NULL constraint to a column of an existing MySQL table with the help of ALTER TABLE statement. SyntaxALTER TABLE table_name MODIFY colum_name datatype NOT NULL; Examplemysql> Create table test123(ID INT, Date DATE); Query OK, 0 rows affected (0.19 sec) mysql> Describe test123; +-------+---------+------+-----+---------+-------+ | Field | Type    | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | ID    | int(11) | YES  |     | NULL    |       | | Date  | date    | YES  |     | NULL    |       | +-------+---------+------+-----+---------+-------+ ... Read More

Actually, MySQL NOT NULL constraint restricts a column of the table from having a NULL value. Once we applied NOT NULL constraint to a column, then we cannot pass a null value to that column. It cannot be declared on the whole table i.e., in other words, we can say that NOT NULL is a column level constraint.For declaring a field NOT NULL, we have to use NOT NULL keyword while defining the column in CREATE TABLE statement.Examplemysql> Create table Employee(ID Int NOT NULL, First_Name Varchar(20), Last_name Varchar(20), Designation Varchar(15)); Query OK, 0 rows affected (0.59 sec)In the query above, ... Read More

Following are few limitations of using SAP HANA Smart Data Access −Virtual Tables cannot be used in multi node HANA cluster. However, it is possible to access virtual table from one HANA server to other.In SAP HANA, few of Analytical view does not support virtual tables so SDA is not suitable.

Following are major changes are done in SAP HANA SPS07 for Smart Data Access −In later version SPS07, it supports SAP Oracle Database 12c, SAP Sybase Event Stream Processor (ESP) 5.1 SP04 and MSSQL server 2012 version 11 as data sources.In SPS07, it is possible to perform insert/update/deletion for remote databases with some limitations.In SPS06, it was not possible to use BLOB and CLOB data types with virtual tables. In SPS07, SDA now supports BLOBs and CLOBs as column data type of virtual table.SDA has a new feature which will help to check whether SDA installation is done successfully or ... Read More

The database user must assign the corresponding object authorizations to the SAP user −Object privilege: CREATE VIRTUAL TABLE on VIRTUAL_TABLES (SYS)Object privilege: DROP on VIRTUAL_TABLES (SYS)