diff options
Diffstat (limited to 'sql.html.markdown')
| -rw-r--r-- | sql.html.markdown | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/sql.html.markdown b/sql.html.markdown index 19eae60f..c317a433 100644 --- a/sql.html.markdown +++ b/sql.html.markdown @@ -4,6 +4,7 @@ filename: learnsql.sql contributors: - ["Bob DuCharme", "http://bobdc.com/"] - ["Th3G33k", "https://github.com/Th3G33k"] + --- Structured Query Language (SQL) is an [ISO/IEC 9075](https://www.iso.org/standard/63555.html) standard language for creating and working with databases stored in a set of tables. Implementations usually add their own extensions to the language; [Comparison of different SQL implementations](http://troels.arvin.dk/db/rdbms/) is a good reference on product differences. @@ -65,16 +66,16 @@ SELECT DISTINCT title FROM titles ORDER BY title ASC; -- Use the comparison operators (=, >, <, >=, <=, <>) and -- the conditional keywords (AND, OR) to refine your queries. -SELECT * FROM departments WHERE dept_no = 'd001' OR dept_no = 'd002' +SELECT * FROM departments WHERE dept_no = 'd001' OR dept_no = 'd002'; -- Same as above. -SELECT * FROM departments WHERE dept_no IN ('d001', 'd0002') +SELECT * FROM departments WHERE dept_no IN ('d001', 'd002'); -- Opposite of the above. -SELECT * FROM departments WHERE dept_no NOT IN ('d001', 'd0002') +SELECT * FROM departments WHERE dept_no NOT IN ('d001', 'd002'); -- Select in a given range. -SELECT * from departments WHERE dept_no BETWEEN 'd001' AND 'd0002' +SELECT * from departments WHERE dept_no BETWEEN 'd001' AND 'd002'; -- Show the number of rows in the departments table. SELECT COUNT(*) FROM departments; @@ -91,15 +92,15 @@ SELECT COUNT(*) FROM departments WHERE dept_name LIKE '%en%'; -- Retrieve the total number of employees, by department number, -- with the condition of having more than 100 employees. SELECT dept_no, COUNT(dept_no) FROM dept_emp GROUP BY dept_no -HAVING COUNT(dept_no) > 100 +HAVING COUNT(dept_no) > 100; -- Aliases, using the optional keyword AS, can be used for column/table names. SELECT COUNT(A.*) AS total_employees, COUNT(B.*) total_departments -FROM employees AS A, departments B +FROM employees AS A, departments B; -- Common date format is "yyyy-mm-dd". -- However, it can vary according to the implementation, the operating system, and the session's locale. -SELECT * FROM dept_manager WHERE from_date >= '1990-01-01' +SELECT * FROM dept_manager WHERE from_date >= '1990-01-01'; -- A JOIN of information from multiple tables: the titles table shows -- who had what job titles, by their employee numbers, from what @@ -117,7 +118,7 @@ FROM titles INNER JOIN employees ON -- UNION selects distinct rows, UNION ALL selects all rows. SELECT * FROM departments WHERE dept_no = 'd001' UNION -SELECT * FROM departments WHERE dept_no = 'd002' +SELECT * FROM departments WHERE dept_no = 'd002'; -- SQL syntax order is: -- SELECT _ FROM _ JOIN _ ON _ WHERE _ GROUP BY _ HAVING _ ORDER BY _ UNION |