-- 在目标主库执行；仅新增养生课程「正在学习人数」字段，不修改已有业务数据，可重复执行。
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SET @ddl = IF(
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(SELECT COUNT(*) FROM information_schema.COLUMNS
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WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'tcm_health_course'
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AND COLUMN_NAME = 'studying_count') = 0,
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'ALTER TABLE tcm_health_course ADD COLUMN studying_count INT NOT NULL DEFAULT 0 COMMENT ''正在学习人数'' AFTER learn_user_count',
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'SELECT 1');
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PREPARE stmt FROM @ddl;
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EXECUTE stmt;
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DEALLOCATE PREPARE stmt;
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