MySQL中联表查询优化的实战指南

    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    invoicing_group_no VARCHAR(50) NOT NULL COMMENT '开票组编号',
    group_name VARCHAR(100) COMMENT '组名称',
    status TINYINT DEFAULT 1 COMMENT '状态 1-启用 0-禁用',
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    KEY idx_status (status)
) COMMENT='开票组配置表，约1200行数据';

    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    claim_approval_no VARCHAR(50) NOT NULL COMMENT '审批单号',
    approval_status VARCHAR(20) COMMENT '审批状态',
    amount DECIMAL(12,2) COMMENT '审批金额',
    applicant_id BIGINT COMMENT '申请人ID',
    apply_date DATE COMMENT '申请日期',
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    UNIQUE KEY uk_approval_no (claim_approval_no),
    KEY idx_apply_date (apply_date),
    KEY idx_applicant (applicant_id)
) COMMENT='审批主表，约12万行数据';

    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    business_no VARCHAR(50) NOT NULL COMMENT '业务单号',
    invoicing_group_no VARCHAR(50) NOT NULL COMMENT '关联开票组',
    claim_approval_no VARCHAR(50) COMMENT '关联审批单号',
    amount DECIMAL(10,2) COMMENT '金额',
    status TINYINT DEFAULT 0 COMMENT '状态 0-待处理 1-已处理 2-已取消',
    create_user_id BIGINT COMMENT '创建人',
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    UNIQUE KEY uk_business_no (business_no),
    KEY idx_status (status),
    KEY idx_create_user (create_user_id),
    KEY idx_created_at (created_at)
) COMMENT='业务主表，约100万行数据，需关联小表和大表';

SELECT m.*, g.group_name, a.approval_status, a.amount as approval_amount
FROM main_table m
JOIN group_table g ON m.invoicing_group_no = g.invoicing_group_no
JOIN approval_table a ON m.claim_approval_no = a.claim_approval_no
WHERE m.invoicing_group_no = 'GROUP001'
  AND m.status = 1
  AND g.status = 1
ORDER BY m.created_at DESC
LIMIT 100;

INDEX(status, created_at)  -- 适合 WHERE status=1 AND created_at > '2024-01-01'

-- 差索引：范围在前，等值在后  
INDEX(created_at, status)  -- 范围查询会中断索引使用

ALTER TABLE main_table ADD INDEX idx_group_approval (invoicing_group_no, claim_approval_no, status, created_at);

-- 小表：关联字段索引
ALTER TABLE group_table ADD INDEX idx_invoicing_group (invoicing_group_no, status);

-- 大表：关联字段索引
ALTER TABLE approval_table ADD INDEX idx_claim_approval (claim_approval_no);