Count Total Transaction each specific row even if 0
SELECT
    channels.channel AS Payment_Channel,
    COMM_CODE.CODE_NAME AS Payment_Name,
    COUNT(B2C_BUY_LOG.PAY_ID) AS Total_Transaction
FROM (           SELECT 'PC01' channel 
       UNION ALL SELECT 'PC02' 
       UNION ALL SELECT 'PC03' 
       UNION ALL SELECT 'PC04' 
       UNION ALL SELECT 'PC05' 
       UNION ALL SELECT 'PC06' 
       UNION ALL SELECT 'PC07' 
       UNION ALL SELECT 'PC08' 
       UNION ALL SELECT 'PC09') channels
LEFT JOIN B2C_BUY_LOG ON B2C_BUY_LOG.PG_CHANNEL = channels.channel
LEFT /* or INNER */ JOIN B2C_BUY_HIST ON B2C_BUY_LOG.PAY_ID = B2C_BUY_HIST.PAY_ID
INNER /* or LEFT */ JOIN COMM_CODE ON B2C_channels.channel = COMM_CODE.CODE
WHERE B2C_BUY_LOG.RET_CODE = 1
AND B2C_BUY_LOG.PAY_ID LIKE '190220%'
GROUP BY Payment_Channel, Payment_Name;