You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 card_games
【Schema】
# Table: set_translations
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(language:TEXT, Examples: [Chinese Simplified, Chinese Traditional, French]),
(setCode:TEXT, Examples: [10E, 4ED, 5DN]),
(translation:TEXT, Examples: [核心系列第十版])
]
# Table: legalities
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(format:TEXT, Examples: [commander, duel, legacy]),
(status:TEXT, Examples: [Legal, Banned, Restricted]),
(uuid:TEXT, Examples: [5f8287b1-5bb6-5f4c-ad17-316a40d5bb0c])
]
# Table: cards
[
(id:INTEGER, Primary Key, Examples: [41138, 1349, 23810]),
(artist:TEXT, Examples: [Pete Venters, Volkan Baǵa, Justin Sweet]),
(asciiName:TEXT, Examples: [El-Hajjaj, Junun Efreet, Dandan]),
(availability:TEXT, Examples: [mtgo,paper, paper, arena]),
(borderColor:TEXT, Examples: [black, white, borderless]),
(cardKingdomFoilId:TEXT, Examples: [123094, 123095, 123096]),
(cardKingdomId:TEXT, Examples: [122719, 122720, 122725]),
(colorIdentity:TEXT, Examples: [W, B, U]),
(colorIndicator:TEXT, Examples: [U, G, R]),
(colors:TEXT, Examples: [W, B, U]),
(convertedManaCost:REAL, Examples: [7.0, 5.0, 4.0]),
(duelDeck:TEXT, Examples: [a, b]),
(edhrecRank:INTEGER, Examples: [15650, 12702, 11081]),
(faceConvertedManaCost:REAL, Examples: [4.0, 5.0, 6.0]),
(faceName:TEXT, Examples: [Dusk, Dawn, Commit]),
(flavorName:TEXT, Examples: [Godzilla, King of the Monsters]),
(flavorText:TEXT),
(frameEffects:TEXT, Examples: [legendary, nyxtouched, miracle]),
(frameVersion:TEXT, Examples: [2003, 1993, 2015]),
(hand:TEXT, Examples: [1, 0, -2]),
(hasAlternativeDeckLimit:INTEGER, Examples: [0, 1]),
(hasContentWarning:INTEGER, Examples: [0, 1]),
(hasFoil:INTEGER, Examples: [0, 1]),
(hasNonFoil:INTEGER, Examples: [1, 0]),
(isAlternative:INTEGER, Examples: [0, 1]),
(isFullArt:INTEGER, Examples: [0, 1]),
(isOnlineOnly:INTEGER, Examples: [0, 1]),
(isOversized:INTEGER, Examples: [0, 1]),
(isPromo:INTEGER, Examples: [0, 1]),
(isReprint:INTEGER, Examples: [1, 0]),
(isReserved:INTEGER, Examples: [0, 1]),
(isStarter:INTEGER, Examples: [0, 1]),
(isStorySpotlight:INTEGER, Examples: [0, 1]),
(isTextless:INTEGER, Examples: [0, 1]),
(isTimeshifted:INTEGER, Examples: [0, 1]),
(keywords:TEXT, Examples: [First strike, Flying, First strike,Flash]),
(layout:TEXT, Examples: [normal, aftermath, split]),
(leadershipSkills:TEXT),
(life:TEXT, Examples: [-5, -1, 2]),
(loyalty:TEXT, Examples: [6, 3, 4]),
(manaCost:TEXT, Examples: [{5}{W}{W}, {4}{W}, {3}{W}]),
(mcmId:TEXT, Examples: [16165, 16166, 16171]),
(mcmMetaId:TEXT, Examples: [156, 176, 368]),
(mtgArenaId:TEXT, Examples: [74983, 74986, 74987]),
(mtgjsonV4Id:TEXT, Examples: [ad41be73-582f-58ed-abd4-a88c1f616ac3]),
(mtgoFoilId:TEXT, Examples: [27501, 26993, 27473]),
(mtgoId:TEXT, Examples: [27500, 26992, 27472]),
(multiverseId:TEXT, Examples: [130550, 129465, 129470]),
(name:TEXT, Examples: [Ancestor's Chosen, Angel of Mercy, Aven Cloudchaser]),
(number:TEXT, Examples: [1, 2, 7]),
(originalReleaseDate:TEXT, Examples: [2012/12/1, 2006/12/1, 2007/12/1]),
(originalText:TEXT),
(originalType:TEXT, Examples: [Creature - Human Cleric]),
(otherFaceIds:TEXT, Examples: [87f0062a-8321-5c16-960e-a12ce1df5839]),
(power:TEXT, Examples: [4, 3, 2]),
(printings:TEXT),
(promoTypes:TEXT, Examples: [boxtopper,boosterfun, boosterfun, release,buyabox]),
(purchaseUrls:TEXT),
(rarity:TEXT, Examples: [uncommon, common, rare]),
(scryfallId:TEXT, Examples: [7a5cd03c-4227-4551-aa4b-7d119f0468b5]),
(scryfallIllustrationId:TEXT, Examples: [be2f7173-c8b7-4172-a388-9b2c6b3c16e5]),
(scryfallOracleId:TEXT, Examples: [fc2ccab7-cab1-4463-b73d-898070136d74]),
(setCode:TEXT, Examples: [10E, 2ED, 2XM]),
(side:TEXT, Examples: [a, b, c]),
(subtypes:TEXT, Examples: [Human,Cleric, Angel, Bird,Soldier]),
(supertypes:TEXT, Examples: [Legendary, Basic, Legendary,Snow]),
(tcgplayerProductId:TEXT, Examples: [15032, 15033, 15045]),
(text:TEXT),
(toughness:TEXT, Examples: [4, 3, 2]),
(type:TEXT, Examples: [Creature — Human Cleric]),
(types:TEXT, Examples: [Creature, Instant, Enchantment]),
(uuid:TEXT, Examples: [00010d56-fe38-5e35-8aed-518019aa36a5]),
(variations:TEXT, Examples: [b7c19924-b4bf-56fc-aa73-f586e940bd42]),
(watermark:TEXT, Examples: [set (HOU), set (LGN), set (ONS)])
]
# Table: sets
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(baseSetSize:INTEGER, Examples: [383, 302, 332]),
(block:TEXT, Examples: [Core Set, Mirrodin, Kaladesh]),
(booster:TEXT),
(code:TEXT, Examples: [10E, 2ED, 2XM]),
(isFoilOnly:INTEGER, Examples: [0, 1]),
(isForeignOnly:INTEGER, Examples: [0, 1]),
(isNonFoilOnly:INTEGER, Examples: [0, 1]),
(isOnlineOnly:INTEGER, Examples: [0, 1]),
(isPartialPreview:INTEGER, Examples: [0, 1]),
(keyruneCode:TEXT, Examples: [10E, 2ED, 2XM]),
(mcmId:INTEGER, Examples: [74, 3204, 10]),
(mcmIdExtras:INTEGER, Examples: [3209, 3459, 2587]),
(mcmName:TEXT, Examples: [Tenth Edition, Double Masters, Fourth Edition]),
(mtgoCode:TEXT, Examples: [10E, 2XM, 5DN]),
(name:TEXT, Examples: [Tenth Edition, Unlimited Edition, Double Masters]),
(parentCode:TEXT, Examples: [JMP, MH1, ZNR]),
(releaseDate:DATE, Examples: [2007-07-13]),
(tcgplayerGroupId:INTEGER, Examples: [1, 115, 2655]),
(totalSetSize:INTEGER, Examples: [508, 302, 384]),
(type:TEXT, Examples: [core, masters, expansion])
]
# Table: rulings
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(date:DATE, Examples: [2007-07-15]),
(text:TEXT),
(uuid:TEXT, Examples: [6d268c95-c176-5766-9a46-c14f739aba1c])
]
# Table: foreign_data
[
(id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(flavorText:TEXT),
(language:TEXT, Examples: [German, Spanish, French]),
(multiverseid:INTEGER, Examples: [148411, 150317, 149934]),
(name:TEXT, Examples: [Ausgewählter der Ahnfrau]),
(text:TEXT),
(type:TEXT, Examples: [Kreatur — Mensch, Kleriker]),
(uuid:TEXT, Examples: [5f8287b1-5bb6-5f4c-ad17-316a40d5bb0c])
]
【Foreign keys】
set_translations.setCode=sets.code
legalities.uuid=cards.uuid
rulings.uuid=cards.uuid
foreign_data.uuid=cards.uuid

    【Question】
    What is the  unconverted mana do all the cards created by Rob Alexander cost in total? unconverted mana refer to manaCost; Rob Alexander refer to artist

    【Evidence】
    unconverted mana refer to manaCost; Rob Alexander refer to artist

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT manaCost FROM cards WHERE artist = 'Rob Alexander'