Sometimes we need a little reminder, below is a  lookup sheet for some the more common commands, and how to use them.

 

Types

CHAR(n)
CHARACTER(n)

 Fixed length string of character n.

VARCHAR2(n)

 Character string of maximum length n, but of varying size.

NUMBER

 Integers.

NUMBER(p,s)

 Numbers of precision p, with s digits after the decimal point.

DATE

 Date information.

TIME

 Time information.

BLOB

 Binary Large Object.

CLOB

 Character binary large object.

NCLOB

 National character sets.

BFILE

 Read only external file.

RAW/LONG RAW

 Binary data, used for import and export.

 

Conversions

to_char(x)
to_number(x)
to_date(x)

 Converts it’s argument to the appropiate type.

to_multi_byte()
to_single_byte()

 Converts between single & multi byte international strings.

chartorowid(x)
rowidtochar(x)

 Converts character strings to ROWID’s & back.

hextoraw(x)
rawtohex(x)

 Converts between hex and RAW binary format (see types).

 

Operators

=,>,<,>=,<=,!=,<>

 Usual comparisons. != & <> & ^= are all negative equality tests.

AND OR NOT

 Boolean operations.

BETWEEN

 SELECT emp_id, name, dept_no FROMepmployee WHEREemp_id BEWTEEN1 AND4;

IN

 SELECT emp_id, name, dept_no FROMepmployee WHERE emp_id IN (1,2,3,4);

LIKE

 Regexp match. % = n characters, _ = 1 character, \ escapes.

 

Constraints

NULL/NOT NULL

 Allow/don’t allow missing values.

[CONSTRAINT <constraint name>
UNIQUE (<column_name>,..)]

 For candidate keys – alternatives to primary key.

PRIMARY KEY

 This is the key field for lookup.

[CONSTRAINT<constraint_name>
CHECK (condition)];

 Verification/validation.

FOREIGN KEY

 This is an index to another table.

 

Single Valued Functions

lpad(<string>,<width>,[<char>]); rpad(<string>,<width>,[<char>]);

 Pad a string to the right or left with the given width with the given char.

lower(<string>);uppper(<string>);initcap(<string>);

 Uppercase, lowercase, or inital upcase the string.

length(<string>);

 Returns length, in chars of the string.

substr(<string>,<start>,<end>);

 Returns a substring from start index, to end index.

abs(<number>)sign(<number>)

 Absolute value and sign number.

ceil(<number>)floor(<number>)

 Ceiling and floor: Highest and lowest integer with smallest difference from float.

mod(<number0>,<number1>)round(<number0>,<number1>)trunc(<number0>,<<number1>)

 Remainder of x / y; Round x to y decimal places. Truncate x to y decimal places

sqrt(<number>)

 Square root.

greatest(<experession>,..)least(<expression>,…)

 Largest and smallest from a list of dates, numbers or strings.

vsize(<expression>)

 The storage size in bytes for x.

sysdate()

 Current system date

add_months(<date>,<integer>)

 Add given number of month to dates;

last_day(<date>)

 Return the last day of the month.

months_between(<date0>,<date1>)

 Return the number of months betwwen two dates/

new_time(<date>,<current_timezone>,
<other_timezone>)

 Convert date from one timezone to another.

nvl(<column>,<value>)

 Substitute <value> for NULL in the column.

soundex(x)

 Return soundex string for fuzzy matching.

decode(<column>,<value>,
<return>,<value>,<return>…)

 For every instance of <value> in column return the matching <return> value. A bit like a case/switch.

 

Creating and Deleting Tables

CREATE TABLE<table name>
(<column definition list>,
(<column name>));  

 CREATE TABLE part
(part_number CHAR(4), part_name VARCHAR(25),PRIMARY_KEY(part_number));

CREATE TABLE<table name>
( <colum_definition [ <constraint > ],  ..);

 CREATE TABLE department
(department_number CHAR(4)
CONSTRAINT prim_dept PRIMARY_KEY,
department_name VARCHAR2(10));

DROP TABLE<table_name>;

 Delete table from database.

 

Changing Tables.

ALTER TABLE<table_name>
ADD(CONSTRAINT <constriant_name>PRIMARY_KEY (<column_names>));

 Creates a primary key constraint for a column.

ALTER TABLE <table_name>
ADD(<colmn_definition>);

 ALTER TABLEemployee
ADD(department_number VARCHAR(12));

ALTER TABLE <table_name>
ADD (CONSTRAINT <constraint_name>FOREIGN_KEY(<colum_name>)
REFERENECESforiegn_table_name(<foreign_column_name>)[ON DELETE CASCADE]);

 Creates a foreign key constraint for a column, mapping to a column on another table. Optional ON DELETE CASCADEmaintains referential integrity by deleting rows in table when row in foreign table is deleted.

ALTER TABLE
DISABLE CONSTRAINT name;

 Relax constraint.

ALTER_TABLE
DROP CONSTRAINT<constraint_name>;

 Delete constraint forever.

 

Modifying and deleting rows

INSERT INTO<table_name>
(<colum_name, ..>)VALUES (<value, ..>);

  INSERT INTO employee
(employee_number, employee_name, salary)
VALUES (‘7092’, ‘FORD’, 175,66);

UPDATE<table_name>
SET <column> =<value>, ..
WHERE <condition>;

 UPDATE wine_list
SET note = ”Ideal as an aperitif’
WHERE wine_name = ‘Ch.Haut-Rian’;

DELETE FROM<table_name>
[WHERE <conditon>]

 DELETE FROM members
WHERE name
LIKE ‘Sharon%’;

 

Querying with Select.

Project and Join.
SELECT <columns> FROM <table>
WHERE <criterion>;

 SELECTemp_table.emp_id, emp_table.dept_no, dept_table.description
FROMemployee_db.emp_table, employee_db.dept_table
WHEREemp_table.dept_no = dept_table.dept_no;

Sorting.
SELECT .<clauses>
ORDER BY <column [DESC|ASC],..>;

 SELECT *
FROM emp
ORDER BY empid DESC; -or- SELECT empid, lastname
FROM emp
ORDER BY 2;

Grouping.
SELECT <select_clauses>
GROUP BY <column [DESC|ASC]..>
HAVING <criterion>;

 SELECT dept, AVG(salary)
FROM emp
GROUP BY dept 
HAVINGavg(salary)>80000
ORDER BY avg(salary)DESC;

Column concatenation – formatting.
SELECT <column>||<string>||<column> <column_alias>… …;

 SELECTfirstname||’,’||lastname full_name
FROM team;

On the fly calculations.
SELECT <expression> FROM DUAL;

 SELECT 7 * 9
FROM DUAL;

Column aliasing.
SELECT <column>
AS <alias_column>..;

 SELECT name, NVL(spouse,’unmarried’)
AS spouse
FROMemp_db,emp_table;

Subqueries.
SELECT …
WHERE column = (<subquery>);,

 SELECT empid, dept, salary
FROM emp
WHERE dept = (
    SELECT dept
    FROM emp
    WHERE empid = 78483);

 

Group functions.

avg()
stddev()
variance()

   Average of all numbers in column.
Standard deviation f all numbers in column.
Variance of all numbers in column.

sum(x)
count(x)

   Sum  total of all numbers in the column.
Toal number of items in a culumn.

max(x)
min(x)

   Maximum value found in a column.
Minimum value found in column.