-- Select all columns
SELECT * FROM table_name;

-- Select specific columns
SELECT column1, column2 FROM table_name;

-- Column aliases
SELECT column1 AS "Alias Name" FROM table_name;

-- Distinct values
SELECT DISTINCT column1 FROM table_name;

-- Limit rows
SELECT * FROM table_name FETCH FIRST 10 ROWS ONLY;

-- Comparison operators
WHERE column = value
WHERE column > value
WHERE column BETWEEN value1 AND value2
WHERE column IN (value1, value2, value3)
WHERE column LIKE 'pattern%'
WHERE column IS NULL

-- Logical operators
WHERE condition1 AND condition2
WHERE condition1 OR condition2
WHERE NOT condition

-- Ascending order (default)
ORDER BY column1;

-- Descending order
ORDER BY column1 DESC;

-- Multiple columns
ORDER BY column1 ASC, column2 DESC;

COUNT(*)           -- Count rows
COUNT(column)      -- Count non-null values
SUM(column)        -- Sum values
AVG(column)        -- Average value
MAX(column)        -- Maximum value
MIN(column)        -- Minimum value

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING COUNT(*) > 5;

-- INNER JOIN
SELECT * FROM table1
INNER JOIN table2 ON table1.id = table2.id;

-- LEFT JOIN
SELECT * FROM table1
LEFT JOIN table2 ON table1.id = table2.id;

-- Multiple joins
SELECT * FROM table1
INNER JOIN table2 ON table1.id = table2.id
INNER JOIN table3 ON table2.id = table3.id;

UPPER(column)          -- Convert to uppercase
LOWER(column)          -- Convert to lowercase
CONCAT(str1, str2)     -- Concatenate strings
SUBSTR(column, 1, 5)   -- Extract substring
LENGTH(column)         -- Get string length
TRIM(column)           -- Remove spaces

SYSDATE                      -- Current date/time
ADD_MONTHS(date, n)          -- Add months
MONTHS_BETWEEN(date1, date2) -- Difference in months
TRUNC(date)                  -- Remove time portion

ROUND(number, decimals)  -- Round number
TRUNC(number, decimals)  -- Truncate number
MOD(number, divisor)     -- Modulus
ABS(number)              -- Absolute value