Structured Query Language CaseEssay Preview: Structured Query Language CaseReport this essayIntroductionSQL (Structured Query Language) is a programming language that is widely utilized in accessing and managing relational database systems. It does creation, updating, deletion, insertion, sorting and plenty of other operations to a database, as well as to the tables and views inside the database.
The execution of SQL commands is based on relational database management system (RDBMS), a database management system. Many different versions of SQL are being run on different RDBMS in todays world. Some of the frequently heard RDBMS are MySQL, Microsoft SQL Server, and Oracle Database, etc.
Developed by the PostgreSQL Global Development Group, PostgreSQL is a “powerful, open source object-relational database system” (About Postgres, the PostgreSQL Global Development Group, 1996-2012). As PostgreSQL derives the majority of its syntax from SQL:2008, it largely complies with the ANSI (American National Standards Institute) standards. PgAdmin, an open source GUI (graphical user interface), is the administration tool for PostgreSQL. The version of the PostgreSQL mentioned in this report is 9.0.
The report is based on the premise that the readers possess the fundamental knowledge in SQL, which includes the SQL statements (SELECT * FROM *, INSERT INTO, UPDATE, DELETE), clauses (WHERE, TOP), operators (AND, OR, LIKE), and keywords (JOIN, ORDER BY). Though not required, readers are recommended to have a junior level of relative experience in programming with SQL.
Basic Control Flow in PostgreSQLThe if-then statement should be a familiar statement for computer programmers of all levels. Although the syntax may vary in different programming languages, it is undoubtedly the most basic control flow statement of all.
In PostgreSQL, one of the ways to apply the most basic control flow is:CASE WHEN (conditional statement) THEN (value returned)[WHEN (conditional statement) THEN (value returned)]ELSE (value returned)ENDThe conditional statement denotes a condition that returns boolean value. The value returned refers to the resulting value when the conditional statement evaluates to true.
The following example decodes the account status of personal bank accounts, assuming that 0 means Active, 1 means Inactive, and 2 means Temporarily Frozen.
SELECT Account_Number,CASE account_statusWHEN 0 THEN ActiveWHEN 1 THEN InactiveWHEN 2 THEN Temporarily FrozenFROM account_tableThe output of the above query will be the readable string account status, instead of a mere digit, that corresponds to each bank account number.Also, a conditional expression can be put inside another conditional expression:CASE WHEN (conditional statement) THEN (CASE WHEN (conditional statement) THEN (value returned)[WHEN (conditional statement) THEN (value returned)]ELSE (value returned)END)[WHEN (conditional statement) THEN (value returned)]ELSE (value returned)ENDThe lines highlighted in shaded color is a complete CASE WHEN statement, which will be executed only if its conditional statement returns true. In that case, the value returned for the highlighted lines will be the ultimate result of the entire statements.
The SQLite3 SQLite3 API
What happens if a particular value is given that appears only when the expression evaluates to YES or NO?
Where is my input value?
In this table, a value was passed to the function where the variable is taken. The value will be stored anywhere in the database regardless of whether the value is stored at a particular place or across different databases.
The column you are viewing in the SQLite3 API should be
\t\tSELECT Account_Number FROM Account_Set where Account_Number
Where $ Account_Number is the account number provided in the SQLite3 API.
You can use the WHERE clause of query statements to select from a pool of values. You need not use a list.query() if you want to keep multiple values in different records.
// SQLQuery
This SQL statement may be executed only in relation to the selected data in the pool.
This SQL statement can also be performed as an output value column.
\end{query}
The SQL query returned by a query is stored across all available databases.
The SQLite3 SQLite3 API
What happens if a particular value is given that appears only when the expression evaluates to YES or NO?
Where is my input value?
In this table, a value was passed to the function where the variable is taken. The value will be stored anywhere in the database regardless of whether the value is stored at a particular place or across different databases.
The column you are viewing in the SQLite3 API should be
\t\tSELECT Account_Number FROM Account_Set where Account_Number
Where $ Account_Number is the account number provided in the SQLite3 API.
You can use the WHERE clause of query statements to select from a pool of values. You need not use a list.query() if you want to keep multiple values in different records.
// SQLQuery
This SQL statement may be executed only in relation to the selected data in the pool.
This SQL statement can also be performed as an output value column.
\end{query}
The SQL query returned by a query is stored across all available databases.
Concatenation in PostgreSQLData retrieved by SQL is always presented in a table format, as presented below:Query:SELECT Last_Name, First_Name, IncomeFROM EmployeesTable:Last_NameFirst_NameIncomeJohnsonPeter$100,000WilliamsNicole$120,000Crisp$98,000At times, users may find it necessary to merge two fields of data into one. While a more literal function CONCAT() is being used to concatenate multiple fields together in some other versions of SQL languages, PostgreSQL uses the concatenation operator (||) to accomplish the same goal. For example, if a user would like to have the Last_Name and First_Name fields combined into a new field called Full_Name, as shown below:
Full_NameIncomeJohnson, Peter$100,000Williams, Nicole$120,000Crisp, Adam$98,000The query should be:SELECT (Last_Name || , || First_Name) AS Full_Name, IncomeFROM Employeeswhere the new field, Full_Name, is denoted as (Last_Name || , || First_Name).It is worth noticing that the concatenation operator works for both string and non-string data types. With that being said, integers could be formatted in a similar manner. A good example would be a table column that demonstrates the market value of a company v.s. the total market value of the entire industry. The table column may be constructed as:
(Company_Market_Value || / || Industry_Market_Value).Truncate a Time to a Specific PrecisionOn some occasions, developers may be required to group the data by day, month or year. In such cases, they presumably need to remove a portion of time from a timestamp field. For example, if the timestamp field returns 2012-08-03