详解SQL高效去除空格的6种方法

-- 去除字段左侧的空格
SELECT 
    original_name,
    -- LTRIM函数只去除字符串左侧的空格
    LTRIM(original_name) AS trimmed_left_name,
    -- 查看原始长度和去除左侧空格后的长度对比
    LENGTH(original_name) AS original_length,
    LENGTH(LTRIM(original_name)) AS left_trimmed_length
FROM customer_data
WHERE original_name LIKE ' %'; -- 筛选出左侧有空格的记录

-- 结合其他函数使用
SELECT 
    first_name,
    last_name,
    -- 先去除左侧空格，再进行拼接
    CONCAT(LTRIM(first_name), ' ', LTRIM(last_name)) AS full_name_cleaned
FROM messy_customer_data;

-- 去除字段右侧的空格
SELECT 
    product_code,
    description,
    -- RTRIM函数只去除字符串右侧的空格
    RTRIM(product_code) AS clean_product_code,
    -- 去除描述字段右侧的空格
    RTRIM(description) AS clean_description,
    -- 显示处理前后的长度差异
    LENGTH(product_code) AS original_code_length,
    LENGTH(RTRIM(product_code)) AS cleaned_code_length
FROM inventory
WHERE product_code LIKE '% '; -- 筛选出右侧有空格的记录

-- 在WHERE条件中使用RTRIM进行精确匹配
SELECT *
FROM products
WHERE RTRIM(product_name) = 'iPhone 14 Pro';

-- 去除字段两侧的空格（最常用的方法）
SELECT 
    user_input,
    -- TRIM函数同时去除字符串前后的空格
    TRIM(user_input) AS clean_input,
    -- 显示处理效果
    CONCAT('[', user_input, ']') AS original_with_brackets,
    CONCAT('[', TRIM(user_input), ']') AS cleaned_with_brackets
FROM form_submissions
WHERE user_input LIKE ' % ' OR user_input LIKE '% '; -- 包含前后空格的记录

-- 更新表中数据，永久去除空格
UPDATE customer_addresses
SET 
    street_address = TRIM(street_address),
    city = TRIM(city),
    state = TRIM(state)
WHERE 
    street_address LIKE ' %' OR street_address LIKE '% ' OR
    city LIKE ' %' OR city LIKE '% ' OR
    state LIKE ' %' OR state LIKE '% ';

-- 使用标准SQL语法明确指定去除方向
SELECT 
    data_field,
    -- 去除两侧空格的标准语法
    TRIM(BOTH FROM data_field) AS both_sides_trimmed,
    -- 只去除前导空格的标准语法
    TRIM(LEADING FROM data_field) AS leading_trimmed,
    -- 只去除尾随空格的标准语法
    TRIM(TRAILING FROM data_field) AS trailing_trimmed
FROM raw_data_table;

-- 使用TRIM去除自定义字符（部分数据库支持）
SELECT 
    phone_number,
    -- 去除电话号码前后的连字符和空格
    TRIM(BOTH '-' FROM TRIM(phone_number)) AS clean_phone
FROM contact_info;

-- MySQL中的去空格方法
SELECT 
    text_column,
    -- 基本TRIM用法
    TRIM(text_column) AS standard_trim,
    -- 去除多个连续空格为单个空格（需结合其他函数）
    REGEXP_REPLACE(TRIM(text_column), '[[:space:]]+', ' ') AS single_spaces_only
FROM mysql_table;

-- SQL Server中的去空格方法
SELECT 
    text_field,
    -- 基本TRIM用法
    TRIM(text_field) AS standard_trim,
    -- LTRIM和RTRIM组合使用
    LTRIM(RTRIM(text_field)) AS combined_trim,
    -- 去除中间多余空格的复杂处理
    REPLACE(REPLACE(REPLACE(LTRIM(RTRIM(text_field)), '  ', ' '), '  ', ' '), '  ', ' ') AS extra_spaces_removed
FROM sql_server_table;

-- Oracle中的去空格方法
SELECT 
    varchar_field,
    -- 标准TRIM用法
    TRIM(varchar_field) AS standard_trim,
    -- 使用REGEXP_REPLACE去除所有类型的空白字符
    REGEXP_REPLACE(varchar_field, '^[[:space:]]+|[[:space:]]+$', '') AS regex_trim
FROM oracle_table;

-- 数据清洗场景：清理导入的数据
SELECT 
    raw_customer_name,
    raw_email,
    raw_phone,
    -- 清理客户姓名
    TRIM(raw_customer_name) AS clean_customer_name,
    -- 清理邮箱地址
    LOWER(TRIM(raw_email)) AS clean_email,
    -- 清理电话号码（去除空格和连字符）
    REPLACE(REPLACE(TRIM(raw_phone), ' ', ''), '-', '') AS clean_phone
FROM imported_customer_data;

-- 查询优化场景：在WHERE子句中使用TRIM
SELECT *
FROM users
WHERE TRIM(username) = 'john_doe' -- 确保即使原数据有空格也能匹配
   OR TRIM(email) = 'john@example.com';

-- 报表生成场景：美化输出格式
SELECT 
    employee_id,
    -- 确保员工姓名没有多余空格
    TRIM(first_name) || ' ' || TRIM(last_name) AS full_name,
    -- 清理部门名称
    TRIM(department_name) AS clean_department
FROM employee_view
ORDER BY TRIM(last_name), TRIM(first_name); -- 排序时也使用TRIM确保准确性