Lesson 11 and 12 ICT

• A relational database management system (RDBMS) provides a way of joining two or more tables with the use of different Structured Query Language (SQL) Join commands.
• The JOIN Commands are used to combine rows from two or more tables.
• A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
• JOIN conditions can be specified using either FROM or WHERE clauses; specifying them in the FROM clause is recommended.
• WHERE and HAVING clauses can also contain search conditions to further filter the rows selected by the join conditions.
• Inner join it is the typical join operation, which uses some comparisison operator like = or <>.
• Outer join it can be a left, right or full outer join.
• Left join or Left outer join the result-set of a left outer join includes all the rows from the left table specified in the left outer clause, not just the ones in which the joined columns match.
• Right join or right outer join is the reverse of a left outer join.
• Null values are returned for the left table any time a right table row has no matching row in the left table.
• A full outer join returns all rows in both the left and right tables.
• Cross join returns all rows from the left table. Cross joins are also called Cartesian products.
• Cartesian products multiply the value of one table to joined table.
• The Verify SQL Syntax will let you validate if the SQL commands are connect or not.
• to determine how many records are produced by the given SQl Query. click Execute SQL
• The SELECT COMMAND will enable you to view the content of you tables.
• The WHERE clause in SQl commands is called filters, which are used when a series of conditions is added.
• An operator is a symbol or a reserved word specifying an action which evaluates the value expression either true or false and performs arithmetic operations.
• Conditional operators are also called comparison operators. They evaluate whether or not the given expressions yield to a true or false value.
• Comparison operators can be used in all expressions except for those with text, ntext, or image data types.
• Logical operators connect two expressions and test their conditional values.
• The AND operator was used to display records with the grades between 85 and 99.
• The Or operator displays a record that meets either or both conditions.
• Null values are returned for the table table any time a right table row has no matching row in the left table. What kind of join is this?

  Left join
• Any time a row has no match in the other table, the select list columns from the other table contain null values. when there is a match between the tables, the entire result set row contains data values from the base table. What kind of join is this?

  Inner join
• When a row in the left table has no matching rows in the right tables, the associated result set row contains null values for all select list columns coming from the right table. What kind of join is this?

  Right join
• A/An Alias is used to give a table or column name a temporary name or nickname during query execution
• It can be left, right, or full. Outer join
• It returns all rows from the left table, each row from the left table is combined with all row from the right table. It is also called Cartesian products. Cross join
• With the aid of the SELECT clause, you can generate accurate and reliable reports.
• Inner join does not allow adding columns with common names
• It uses a comparison operator to match rows from two tables based on the values in common columns from each table