Zechariah 12 is not about Jesus 

Zechariah 12 prophesies a future battle where Israel will be victorious. The context of the verse is that people are slain/pierced in battle and that the people of Jerusalem will have compassion on them and lament to God about them. You can see this if the verse is read in context: 

Zechariah 12:9 In that day I will all but annihilate all the nations that came up against Jerusalem. 10 But I will fill the House of David and the inhabitants of Jerusalem with a spirit of pity and compassion; and they shall lament to Me about those who are slain, wailing over them as over a favourite son and showing bitter grief as over a first-born.